Major Depressive Disorder, Bipolar Disorder & Schizophrenia — Clinical Compendium

MDD (SIGECAPS)

≥5 of 9 symptoms (including depressed mood or anhedonia) for ≥2 weeks: Sleep, Interest, Guilt, Energy, Concentration, Appetite, Psychomotor, Suicidality.

Bipolar I vs. Bipolar II

Bipolar I requires ≥1 full Manic episode (≥7 days or any duration if hospitalized/psychotic). Bipolar II requires ≥1 Hypomanic episode (≥4 days) AND ≥1 Major Depressive episode.

Schizophrenia Timeline

Brief Psychotic Disorder (<1 month) → Schizophreniform Disorder (1 to 6 months) → Schizophrenia (≥6 months total duration with ≥1 month active psychosis).

Serotonin Syndrome vs. NMS

Serotonin Syndrome: Hyperreflexia, inducible ankle clonus, myoclonus, diarrhea (Rx: Cyproheptadine). NMS: 'Lead-pipe' rigidity, hyporeflexia, elevated CK (Rx: Dantrolene).

Schizoaffective vs. Mood + Psychosis

Schizoaffective requires ≥2 weeks of delusions or hallucinations in the Complete Absence of a major mood episode, plus mood episodes present for the majority of the illness.

Antipsychotic EPS Timeline

Acute Dystonia (hours–days: torticollis/oculogyric crisis) → Akathisia (days–weeks: restlessness) → Parkinsonism (weeks–months) → Tardive Dyskinesia (months–years).

Lithium Nephrotoxicity & Teratogenicity

Inhibits ADH signaling in principal cells causing Nephrogenic Diabetes Insipidus (treat with Amiloride); causes hypothyroidism, fine tremor, and Ebstein anomaly.

Bupropion & Mirtazapine Pearls

Bupropion (NDRI): Zero sexual side effects, aids smoking cessation, lowers seizure threshold (contraindicated in bulimia/anorexia). Mirtazapine: Alpha-2 antagonist, increases appetite/sleep.

Depressive & Bipolar Disorders Diagnostic Rubric

DSM-5-TR classification of depressive, bipolar, and psychotic spectrum disorders relies on strict chronological duration cutoffs, symptom count thresholds, and degree of functional impairment or psychosis. Mastering the timeline rules separating Major Depressive Disorder, Persistent Depressive Disorder, Bipolar I vs. II, Cyclothymia, and the Schizophrenia spectrum (Brief Psychotic Disorder vs. Schizophreniform vs. Schizophrenia vs. Schizoaffective Disorder) prevents diagnostic misclassification on board vignettes.

Disorder	Core Diagnostic Criteria	First-Line Pharmacotherapy
Major Depressive Disorder	≥ 5 of 9 SIGECAPS symptoms for ≥ 2 weeks with functional impairment	SSRI (Sertraline, Escitalopram) or SNRI (Venlafaxine, Duloxetine) + CBT
Bipolar I Disorder	≥ 1 manic episode (≥ 7 days of DIGFAST criteria: Distractibility, Impulsivity, Grandiosity, Flight of ideas, Activity increase, Sleep decrease, Talkativeness)	Mood Stabilizer: Lithium, Valproate, or Second-Generation Antipsychotic (Quetiapine, Aripiprazole)
Bipolar II Disorder	≥ 1 hypomanic episode (≥ 4 days, noticeable change but no hospitalization or psychosis) + ≥ 1 major depressive episode	Quetiapine, Lurasidone, Lamotrigine, or Lithium
Persistent Depressive Disorder (Dysthymia)	Depressed mood most days for ≥ 2 years (≥ 1 yr in children) with ≥ 2 depressive symptoms	SSRIs + Psychotherapy

Depressive vs. Bipolar Spectrum Chronology: SIGECAPS, DIGFAST & Bipolar I (1 Week Mania) vs. Bipolar II (4 Days Hypomania)

Major Depressive Disorder (MDD) requires ≥5 of 9 SIGECAPS symptoms for ≥2 consecutive weeks, including either depressed mood or anhedonia (Sleep disturbance, Interest loss [anhedonia], Guilt/worthlessness, Energy loss/fatigue, Concentration impairment, Appetite/weight change, Psychomotor retardation/agitation, Suicidal ideation). Notice the critical subtype: MDD with Atypical Features presents with mood reactivity (mood brightens in response to positive events), hypersomnia, hyperphagia, 'leaden paralysis' (heavy limbs), and interpersonal rejection sensitivity—uniquely responsive to MAO Inhibitors (phenelzine, tranylcypromine) or SSRIs. Persistent Depressive Disorder (Dysthymia) requires depressed mood plus ≥2 depressive symptoms for ≥2 years in adults (≥1 year in children/adolescents) without more than 2 symptom-free months. On the bipolar spectrum (mnemonic DIGFAST: Distractibility, Indiscretion/impulsivity, Grandiosity, Flight of ideas, Activity increase, Sleep deficit [decreased need for sleep, not insomnia], Talkativeness/pressured speech), Bipolar I Disorder requires at least one Manic Episode lasting ≥7 days (1 week)—or any duration if hospitalization is required or psychotic features are present—causing marked social/occupational impairment (a major depressive episode is common but NOT required for Bipolar I diagnosis!). Conversely, Bipolar II Disorder requires at least one Hypomanic Episode lasting ≥4 consecutive days AND at least one Major Depressive Episode, where hypomania lacks psychotic features, never requires hospitalization, and does not cause marked functional impairment. Cyclothymic Disorder is ≥2 years (≥1 year in youth) of fluctuating hypomanic and depressive symptoms that never meet full criteria for hypomania or MDD. Never prescribe antidepressant monotherapy in Bipolar I or II without a mood stabilizer (Lithium, Valproate, Lamotrigine, or Second-Generation Antipsychotic), as unopposed antidepressants precipitate rapid cycling and acute mania!

The Psychotic Timeline (<1 Month vs. 1–6 Months vs. >=6 Months) & Schizoaffective vs. Mood Disorder with Psychotic Features

Primary psychotic disorders (requiring ≥2 of 5 core symptoms, including at least one of the first three: [1] Delusions, [2] Hallucinations, [3] Disorganized speech, [4] Grossly disorganized or catatonic behavior, [5] Negative symptoms [flat affect, avolition, alogia]) are differentiated strictly by total duration from symptom onset: (1) Brief Psychotic Disorder lasts ≥1 day to <1 month, with complete return to baseline functioning; (2) Schizophreniform Disorder lasts ≥1 month to <6 months; and (3) Schizophrenia lasts ≥6 months (including at least 1 month of active-phase symptoms plus prodromal/residual symptoms). One of the most frequently tested psychiatric board distinctions separates Schizoaffective Disorder from Major Depressive or Bipolar Disorder with Psychotic Features: both present with concurrent mood episodes (depression or mania) and psychotic symptoms (delusions/hallucinations). However, in Mood Disorder with Psychotic Features, psychotic symptoms occur EXCLUSIVELY during a major depressive or manic episode (never when the patient is euthymic). In contrast, Schizoaffective Disorder requires a lifetime history of ≥2 weeks of delusions or hallucinations in the COMPLETE ABSENCE of a major mood episode, alongside mood episodes that are present for the majority of the total duration of the illness!

Life-Threatening Psychiatric Emergencies: Serotonin Syndrome vs. NMS

Serotonin Syndrome and Neuroleptic Malignant Syndrome (NMS) are life-threatening pharmacologic toxidromes presenting with the shared tetrad of hyperthermia, autonomic instability, altered mental status, and neuromuscular hyperactivity. Rapidly differentiating serotonergic neuromuscular clonus and hyperreflexia from dopaminergic 'lead-pipe' rigidity and rhabdomyolysis is critical to administer the correct antidote (cyproheptadine vs. dantrolene).

Feature	Serotonin Syndrome	Neuroleptic Malignant Syndrome (NMS)
Precipitating Agents	SSRIs, SNRIs, TCAs, MAOIs, Tramadol, Linezolid, MDMA (Ecstasy), St. John's Wort	D2-receptor antagonists (Haloperidol, Fluphenazine, Risperidone) or Dopamine agonist withdrawal
Onset Speed	Rapid (within 24 hours of initiation or dose increase)	Subacute (develops over 1-3 days to weeks)
Neuromuscular Tone	Hyperreflexia, spontaneous / inducible clonus, tremor, shivering	'Lead-pipe' muscle rigidity, hyporeflexia, bradykinesia
Gastrointestinal	Hyperactive bowel sounds, diarrhea, nausea	Normal or hypoactive bowel sounds
Specific Antidote	Cyproheptadine (5-HT2A antagonist)	Dantrolene (ryanodine antagonist) or Bromocriptine (dopamine agonist)

Neuromuscular Examination: Ankle Clonus & Hyperreflexia (Serotonin Syndrome) vs. Lead-Pipe Rigidity (NMS)

When an agitated, febrile, diaphoretic, tachycardic patient on psychotropic medications presents to the emergency department, the lower-extremity neuromuscular examination and onset kinetics immediately separate Serotonin Syndrome from Neuroleptic Malignant Syndrome (NMS): (1) Serotonin Syndrome develops rapidly within 2 to 24 hours of combining two serotonergic agents—such as an SSRI/SNRI with an MAO Inhibitor (including Linezolid or Methylene Blue!), Tramadol, Meperidine, Dextromethorphan, Triptans, MDMA (Ecstasy), or St. John's Wort. Excess 5-HT_1A and 5-HT_2A stimulation in the brainstem and spinal cord produces myoclonus, inducible ankle/ocular CLONUS, lower-extremity predominant HYPERREFLEXIA (4+ DTRs), tremor, mydriasis, and hyperactive bowel sounds with diarrhea. (2) Neuroleptic Malignant Syndrome (NMS) evolves more gradually over 1 to 3 days (up to 2 weeks) after initiating or escalating a Dopamine D₂ receptor antagonist (high-potency first-generation antipsychotics like Haloperidol or Fluphenazine, atypical antipsychotics, or antiemetics like Metoclopramide/Prochlorperazine)—or after abruptly withdrawing Levodopa/Carbidopa in a Parkinson patient! Central nigrostriatal and hypothalamic D₂ blockade produces generalized 'LEAD-PIPE' MUSCLE RIGIDITY, HYPOREFLEXIA or normal reflexes (NEVER clonus!), mutism, malignant hyperthermia (>40°C), and massive skeletal muscle breakdown with Creatine Kinase (CK) >1,000–100,000 U/L and myoglobinuric acute kidney injury.

Targeted Antidote Pharmacology: Cyproheptadine (5-HT2A Blockade) vs. Dantrolene (Ryanodine Receptor) & Bromocriptine

Immediate management of both syndromes begins with discontinuing the offending agent, aggressive intravenous crystalloid resuscitation, external cooling blankets (note: antipyretics like acetaminophen are completely ineffective because hyperthermia is driven by muscular heat generation, not hypothalamic PGE₂ set-point elevation!), and intravenous Benzodiazepines (lorazepam/diazepam) to control agitation and muscle hyperactivity. When severe symptoms persist, administer the specific pharmacologic antidote: for Serotonin Syndrome, administer oral/nasogastric Cyproheptadine, a first-generation antihistamine with potent 5-HT_1A and 5-HT_2A receptor antagonist activity. For Neuroleptic Malignant Syndrome (NMS) (as well as Malignant Hyperthermia triggered by succinylcholine or volatile inhaled anesthetics like halothane/sevoflurane due to autosomal dominant RYR1 mutations), administer intravenous Dantrolene—a direct skeletal muscle relaxant that antagonizes sarcoplasmic reticulum Ryanodine Receptors (RyR1) to halt intracellular Ca²⁺ release and stop muscle contraction/heat generation—and/or oral Bromocriptine (a central dopamine D₂ receptor agonist that restores hypothalamic and nigrostriatal dopaminergic tone). Remember the mandatory 2-week washout rule when switching from an SSRI to an MAOI (5-week washout for Fluoxetine due to the long half-life of its active metabolite, norfluoxetine)!

Psychotic Spectrum Timeline & Differential Diagnosis

Diagnosing primary psychotic disorders on board exams hinges on two strict dimensions: exact symptom duration and the temporal relationship between psychotic symptoms and major mood episodes. Schizophrenia is characterized by dysfunction across three distinct dopaminergic pathways: hyperactivity of the mesolimbic pathway produces positive symptoms (hallucinations, delusions, disorganized speech and behavior), hypoactivity of the mesocortical pathway drives negative and cognitive symptoms (affective flattening, alogia, avolition, anhedonia, asociality—the '5 As'), blockade of the nigrostriatal pathway causes extrapyramidal movement symptoms, and blockade of the tuberoinfundibular pathway removes tonic dopamine (PIF) inhibition of lactotrophs, leading to hyperprolactinemia (galactorrhea, amenorrhea, gynecomastia, and osteopenia). DSM-5 diagnosis of Schizophrenia requires at least 2 of the following 5 symptoms for at least 1 month (with at least one being 1, 2, or 3): (1) Delusions, (2) Hallucinations, (3) Disorganized speech, (4) Grossly disorganized or catatonic behavior, and (5) Negative symptoms, alongside continuous signs of disturbance lasting at least 6 months with marked social or occupational decline.

Psychotic Disorder	Strict Duration Criterion	Core Diagnostic Rule & Mood Overlap	First-Line Management
Brief Psychotic Disorder	≥1 day to <1 month (with complete return to baseline functioning)	Often precipitated by an acute severe psychosocial stressor or postpartum state; ≥1 positive symptom required	Short-term Second-Generation Antipsychotic (risperidone, olanzapine) + supportive psychotherapy
Schizophreniform Disorder	≥1 month to <6 months	Identical symptom criteria to Schizophrenia (≥2 of 5 symptoms), but total duration has not reached 6 months; functional decline not strictly required	Second-Generation Antipsychotic; if symptoms persist past 6 months, reclassify diagnosis as Schizophrenia
Schizophrenia	≥6 months total duration (including ≥1 month of active-phase symptoms)	Must include ≥2 of 5 core symptoms (at least one must be delusions, hallucinations, or disorganized speech) + functional impairment	Lifelong Second-Generation Antipsychotic + cognitive behavioral therapy; long-acting injectable (haloperidol/paliperidone) if non-adherent
Schizoaffective Disorder	≥2 weeks of isolated psychosis WITHOUT mood symptoms + mood episodes present for majority of illness	Requires an uninterrupted period of illness featuring MDD or Mania PLUS ≥2 weeks of delusions/hallucinations when mood is completely euthymic	Antipsychotic (Paliperidone is FDA-approved specifically for schizoaffective) + Mood Stabilizer (Lithium/Valproate) or SSRI
MDD or Bipolar with Psychotic Features	Psychotic symptoms occur EXCLUSIVELY during major depressive or manic episodes	Whenever the patient's depression or mania resolves, delusions and hallucinations completely vanish (never present for 2 weeks without mood symptoms)	Bipolar: Mood stabilizer + Antipsychotic; Psychotic Depression: Antidepressant (SSRI/SNRI) + Antipsychotic OR Electroconvulsive Therapy (ECT)
Delusional Disorder	≥1 month of ≥1 fixed delusion	Non-bizarre or bizarre fixed delusions (erotomanic, grandiose, jealous, persecutory, somatic) WITHOUT hallucinations, disorganized speech, or negative symptoms; daily functioning preserved	Cognitive behavioral therapy + trial of Second-Generation Antipsychotic (often poor insight and medication resistance)

Diagnostic timeline comparing Brief Psychotic Disorder, Schizophreniform Disorder, Schizophrenia, and Schizoaffective Disorder — **Psychotic Spectrum Diagnostic Timeline:** Strict temporal cutoffs (<1 month vs. 1–6 months vs. ≥6 months) and mood-overlap rules separating Schizoaffective Disorder from Mood Disorders with Psychotic Features. View Full Resolution

Schizoaffective Disorder vs. Mood Disorder with Psychotic Features

The single most frequently tested differential in psychotic psychiatry is separating Schizoaffective Disorder from Major Depressive or Bipolar Disorder with Psychotic Features. Always construct a timeline of when the delusions/hallucinations occurred relative to the depressive or manic symptoms. If delusions and hallucinations occur only while the patient is actively depressed or manic, the diagnosis is a Mood Disorder with Psychotic Features. Conversely, if the vignette documents a period of at least 2 consecutive weeks in which the patient experienced delusions or hallucinations in the complete absence of major depressive or manic symptoms—and mood episodes have been present for a substantial majority of the total illness duration—the diagnosis is Schizoaffective Disorder.

Cluster A Personality Disorders vs. True Psychotic Disorders

Patients presenting with eccentric behavior, suspiciousness, or social isolation without frank, sustained hallucinations or fixed delusions belong to the Cluster A ('Weird') Personality Disorders: Paranoid Personality Disorder (pervasive distrust and suspicion of others' motives without fixed psychotic delusions; uses projection as primary defense mechanism), Schizoid Personality Disorder (lifelong voluntary social detachment, preference for solitary activities, emotional coldness, and indifference to praise or criticism—content to be a 'loner'), and Schizotypal Personality Disorder (magical thinking, odd beliefs/superstitions, ideas of reference, eccentric dress/speech, and severe social anxiety driven by paranoid fears that does not abate with familiarity).

Postpartum Blues vs. Postpartum Depression vs. Postpartum Psychosis

Peripartum psychiatric presentations follow a strict severity and timeline gradient: (1) Postpartum Blues affects up to 80% of mothers, begins within 2–3 days of delivery, features tearfulness, mood lability, and fatigue with intact infant bonding and no suicidal/infanticidal ideation, and resolves spontaneously within 10–14 days with reassurance and sleep support; (2) Peripartum (Postpartum) Depression persists beyond 2 weeks (onset during pregnancy or within 4 weeks postpartum), meets full SIGECAPS criteria with guilt or anxiety about caring for the infant, and is treated with SSRIs (sertraline is preferred during breastfeeding) or brexanolone/zuranolone plus psychotherapy; (3) Postpartum Psychosis is an acute psychiatric emergency presenting within the first 2 weeks postpartum (often in patients with underlying Bipolar Disorder) with command hallucinations, delusions that the infant is possessed, severe insomnia, and high risk of infanticide and suicide—requiring immediate inpatient psychiatric hospitalization, mother-infant separation/supervision, antipsychotics, lithium, or ECT.

Antipsychotic Pharmacology: First-Generation vs. Second-Generation Profiles, EPS Timeline & Clozapine Mandates

Antipsychotics are divided into First-Generation (Typical) Antipsychotics (FGAs), which act primarily as post-synaptic dopamine D₂ receptor antagonists, and Second-Generation (Atypical) Antipsychotics (SGAs), which combine lower-affinity D₂ receptor antagonism (or partial agonism in aripiprazole/brexpiprazole/cariprazine) with potent serotonin 5-HT_2A receptor antagonism. High-potency FGAs (haloperidol, fluphenazine, trifluoperazine, pimozide) tightly bind nigrostriatal D₂ receptors and carry the highest incidence of Extrapyramidal Symptoms (EPS) and hyperprolactinemia, whereas low-potency FGAs (chlorpromazine, thioridazine) cause less EPS but potent H₁ (sedation, weight gain), alpha₁-adrenergic (orthostatic hypotension), and muscarinic M₁ (dry mouth, constipation, urinary retention, blurred vision, confusion) blockade—summarized by the mnemonic Cheaper Drugs Are Sedating; Haloperidol Gives Rigidity. Note also their signature ocular toxicities: chlorpromazine causes corneal and lenticular deposits, whereas thioridazine causes vision-threatening pigmentary retinopathy.

EPS / Adverse Syndrome	Typical Onset Window	Pathophysiology & Clinical Presentation	First-Line Pharmacologic Treatment
Acute Dystonia	Hours to Days	Sudden nigrostriatal D2 blockade causing sustained, painful muscle spasms: torticollis, trismus, laryngospasm, or oculogyric crisis (forced upward eye deviation)	Immediate IM/IV Benztropine (muscarinic antagonist) or Diphenhydramine (H1/muscarinic antagonist)
Akathisia	Days to Weeks	Subjective inner restlessness and objective inability to sit still (incessant pacing, leg crossing, rocking back and forth); frequently misdiagnosed as worsening psychotic agitation!	First-line: Beta-blocker (Propranolol) + dose reduction or switch to low-EPS SGA (quetiapine); Benzodiazepines (lorazepam) or benztropine are second-line
Drug-Induced Parkinsonism	Weeks to Months	Nigrostriatal dopamine depletion producing bradykinesia, cogwheel rigidity, shuffling gait, masked facies, and pill-rolling resting tremor	Oral Benztropine or Amantadine (increases dopamine release), or transition from FGA to an atypical antipsychotic
Tardive Dyskinesia	Months to Years	Chronic D2 blockade induces compensatory upregulation and supersensitivity of postsynaptic striatal D2 receptors; involuntary choreoathetoid lip-smacking, grimacing, tongue writhing	Discontinue/switch antipsychotic (to Clozapine or Quetiapine) and administer a VMAT2 inhibitor (Valbenazine or Deutetrabenazine); NEVER give benztropine (worsens TD)
Neuroleptic Malignant Syndrome (NMS)	Anytime (often within first 2 weeks of starting or increasing dose)	Central hypothalamic and nigrostriatal D2 blockade causing 'FEVER': Fever (>40°C), Encephalopathy, Vital sign instability, Elevated CK (>1,000 IU/L; rhabdomyolysis), 'Lead-pipe' Rigidity	Immediately stop antipsychotic, aggressive IV fluid resuscitation, ICU cooling, Dantrolene (ryanodine RYR1 antagonist) or Bromocriptine (D2 agonist)

Chronological timeline of antipsychotic-induced extrapyramidal symptoms and targeted pharmacologic reversal — **Extrapyramidal Symptom (EPS) Progression & Reversal:** Chronological evolution from Acute Dystonia (hours–days) to Akathisia (days–weeks), Drug-Induced Parkinsonism (weeks–months), and Tardive Dyskinesia (months–years), alongside Neuroleptic Malignant Syndrome. View Full Resolution

Second-Generation (Atypical) Antipsychotic Signature Adverse Profiles

Although SGAs reduce EPS incidence via 5-HT_2A antagonism, each agent carries high-yield board toxicities: (1) Olanzapine and Clozapine cause the most severe metabolic syndrome (profound weight gain, insulin resistance/type 2 diabetes mellitus, and hypertriglyceridemia requiring baseline and routine BMI, fasting glucose/HbA1c, and lipid panels); (2) Risperidone and Paliperidone (the active 9-hydroxy metabolite of risperidone) have the highest D₂ affinity among SGAs and are the most notorious causes of hyperprolactinemia (amenorrhea, galactorrhea, gynecomastia, and decreased GnRH/libido); (3) Ziprasidone causes the greatest QTc interval prolongation (risking Torsades de Pointes) and must be taken with a 500-calorie meal for absorption; (4) Quetiapine is highly sedating (H₁ blockade) and carries a classical board association with cataracts in animal studies; and (5) Aripiprazole acts as a D₂ partial agonist, causing minimal weight gain and lowering prolactin, though it frequently causes akathisia.

Clozapine Indications, Agranulocytosis Monitoring & Myocarditis

Clozapine is uniquely indicated for (1) treatment-resistant schizophrenia (failure of at least two adequate trials of different antipsychotics), (2) schizophrenia or schizoaffective disorder with recurrent suicidal behavior, and (3) psychosis in Parkinson disease (alongside pimavanserin and quetiapine). Because clozapine carries a 1% risk of potentially fatal agranulocytosis, patients must enroll in a mandatory registry with weekly Absolute Neutrophil Count (ANC) checks for the first 6 months, biweekly for months 6–12, and monthly thereafter (clozapine must be interrupted immediately if ANC falls below 1,000/mm³). Additional signature clozapine toxicities include myocarditis and cardiomyopathy (suspect in any patient on clozapine developing unexplained tachycardia, fever, chest pain, or dyspnea within the first month), dose-dependent generalized seizures (up to 5% at high doses), severe anticholinergic gastrointestinal hypomotility/ileus, and paradoxical nocturnal sialorrhea (hypersalivation).

Serotonin Syndrome vs. Neuroleptic Malignant Syndrome vs. Malignant Hyperthermia

When an agitated, hyperthermic, tachycardic patient presents to the emergency department, neuromuscular tone and reflex examination immediately differentiate the three hyperthermic drug emergencies: (1) Serotonin Syndrome (triggered by SSRIs/SNRIs combined with MAOIs, linezolid, tramadol, triptans, dextromethorphan, MDMA, or St. John's wort) presents rapidly within 24 hours with hyperreflexia, inducible ankle and ocular clonus, myoclonus, tremor, mydriasis, and hyperactive bowel sounds/diarrhea, and is treated with benzodiazepines and the 5-HT_2A antagonist cyproheptadine; (2) Neuroleptic Malignant Syndrome (antipsychotics or metoclopramide) evolves over days with diffuse 'lead-pipe' muscle rigidity, bradyreflexia/hyporeflexia, normal pupils, and massive CK elevation, and is treated with dantrolene or bromocriptine; (3) Malignant Hyperthermia (succinylcholine or volatile inhaled anesthetics like halothane/sevoflurane in patients with autosomal dominant RYR1 mutations) presents intraoperatively with masseter spasm, abrupt spike in end-tidal CO₂ (ETCO₂), generalized rigidity, and hyperkalemia, and is treated with IV dantrolene.

Bipolar I vs. Bipolar II vs. Cyclothymia & Mood Stabilizer Pharmacology

Accurate classification along the bipolar spectrum depends on distinguishing full mania from hypomania using duration, severity, and psychotic features. Both manic and hypomanic episodes require an abnormally and persistently elevated, expansive, or irritable mood plus increased goal-directed energy/activity accompanied by at least 3 of the 7 DIG FAST symptoms (4 if mood is only irritable): Distractibility, Indiscretion/impulsivity (spending sprees, reckless sexual encounters), Grandiosity, Flight of ideas/racing thoughts, Activity increase (psychomotor agitation), Sleep deficit (decreased need for sleep—feeling fully rested after 2–3 hours, unlike insomnia), and Talkativeness (pressured speech). A Manic Episode lasts ≥7 consecutive days (or any duration if hospitalization is required or psychotic features are present) and causes marked social or occupational impairment; a single lifetime manic episode establishes the diagnosis of Bipolar I Disorder (even without a prior major depressive episode).

Mood Stabilizer	Primary Mechanism of Action	Clinical Indications	High-Yield Adverse Effects & Teratogenicity
Lithium Carbonate	Inhibits inositol monophosphatase (IMPase) and GSK-3beta, depleting intracellular PIP2/IP3/DAG second messengers	First-line for Acute Mania, Bipolar Maintenance, and Bipolar Depression; uniquely reduces suicidality	LMNOP: Lithium side effects — Movement (fine tremor; coarse tremor = toxicity), Nephrogenic DI (polyuria/polydipsia -> Rx: Amiloride), Hypothyroidism (goiter), Maternal teratogen (Ebstein anomaly: atrialized right ventricle), Parathyroid hyperplasia (hypercalcemia)
Valproate (Valproic Acid)	Blocks voltage-gated Na+ channels and increases CNS GABA concentrations by inhibiting GABA transaminase	First-line for Acute Mania, mixed features, and rapid-cycling Bipolar Disorder	Hepatotoxicity (fatal hepatic failure in young children), acute pancreatitis, thrombocytopenia, alopecia, weight gain, and neural tube defects (spina bifida — highest teratogenicity!)
Lamotrigine	Inhibits voltage-gated Na+ channels and suppresses presynaptic glutamate and aspartate release	First-line for Bipolar Maintenance and Bipolar Depression (NOT effective for acute mania)	Life-threatening Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN) — requires slow dose titration and immediate discontinuation if rash develops
Carbamazepine	Blocks inactivated voltage-gated Na+ channels	Second-line for Acute Mania and rapid-cycling Bipolar Disorder; first-line for Trigeminal Neuralgia	Agranulocytosis/aplastic anemia (requires CBC monitoring), SIADH (hyponatremia), potent CYP450 auto-inducer, SJS/TEN (screen HLA-B*1502 in Asian patients), neural tube defects
Second-Generation Antipsychotics (Quetiapine, Lurasidone, Olanzapine, Risperidone)	D2 and 5-HT2A antagonism	First-line for Severe Acute Mania (fastest onset of action) and Bipolar Depression (Quetiapine, Lurasidone, Cariprazine, Olanzapine-Fluoxetine)	Metabolic syndrome (weight gain, diabetes, dyslipidemia), sedation, extrapyramidal symptoms, QTc prolongation

Bipolar II Disorder vs. Cyclothymic Disorder

In contrast to mania, a Hypomanic Episode lasts at least 4 consecutive days, represents an unequivocal change in functioning observable by others, does NOT cause marked social/occupational impairment, does NOT require hospitalization, and NEVER includes psychotic features (any psychosis or hospitalization automatically upgrades the episode to full mania and Bipolar I). Bipolar II Disorder requires at least one lifetime Hypomanic Episode AND at least one lifetime Major Depressive Episode (with zero history of full mania). Cyclothymic Disorder is a chronic, fluctuating mood disturbance lasting ≥2 years (≥1 year in children/adolescents) characterized by numerous periods of hypomanic symptoms and depressive symptoms that never meet the full symptom-count or duration thresholds for a major depressive, manic, or hypomanic episode, with symptom-free intervals lasting no longer than 2 consecutive months.

Lithium Pharmacokinetics, Nephrogenic Diabetes Insipidus & Drug Interactions

Lithium is a monovalent cation handled by the kidney almost identically to sodium: 70–80% of filtered lithium is reabsorbed in the proximal convoluted tubule alongside sodium and water. Consequently, any state of volume depletion, low-sodium diet, or initiation of drugs that induce natriuresis or reduce GFR—specifically thiazide diuretics, NSAIDs, and ACE inhibitors/ARBs—triggers compensatory proximal tubular reabsorption of both sodium and lithium, precipitating acute lithium toxicity (>1.5 mEq/L: GI distress, coarse tremor, ataxia, confusion, seizures, and sinus node bradycardia). Furthermore, lithium enters the principal cells of the cortical collecting duct via epithelial sodium channels (ENaC) and inhibits glycogen synthase kinase-3 (GSK-3) and adenylate cyclase, uncoupling vasopressin (V₂) receptors from aquaporin-2 insertion and causing Nephrogenic Diabetes Insipidus. Blocking ENaC with the potassium-sparing diuretic amiloride prevents lithium entry into principal cells and is the treatment of choice for lithium-induced nephrogenic DI without raising serum lithium levels.

Managing Acute Mania & Bipolar Depression Without Triggering Manic Switch

For severe acute mania with agitation or psychosis, combining a Second-Generation Antipsychotic (risperidone, olanzapine, quetiapine, or aripiprazole)—or IM haloperidol plus lorazepam for emergent agitation—with lithium or valproate provides the fastest clinical stabilization because lithium and valproate require 5 to 14 days to achieve full antimanic efficacy. For Bipolar Depression, first-line FDA-approved options are quetiapine, lurasidone, cariprazine, the olanzapine-fluoxetine combination, or lamotrigine/lithium; antidepressant monotherapy (SSRIs, SNRIs, bupropion, TCAs) is strictly contraindicated because it destabilizes mood and induces a manic switch.

Major Depressive Disorder Subtypes & Antidepressant Pharmacology

Major Depressive Disorder (MDD) requires at least 5 of 9 SIGECAPS symptoms for ≥2 weeks, including either depressed mood or anhedonia (loss of interest or pleasure), after ruling out hypothyroidism, substance/medication effects, and bipolar disorder. Boards test specific clinical subtypes of depression that alter prognostic and therapeutic decisions: MDD with Atypical Features is the most common subtype and is defined by mood reactivity (mood brightens transiently in response to positive events) plus ≥2 of: hyperphagia/weight gain, hypersomnia (≥10 hr/day), leaden paralysis (heavy, weighted sensation in the arms and legs), and lifelong sensitivity to interpersonal rejection; while SSRIs are first-line in modern practice, classic board questions highlight the superior historical efficacy of Monoamine Oxidase Inhibitors (MAOIs: phenelzine, tranylcypromine, isocarboxazid, selegiline) in atypical depression.

Antidepressant Class & Agents	Mechanism of Action	Signature Clinical Indications	Board-Tested Adverse Effects & Contraindications
SSRIs (Fluoxetine, Sertraline, Escitalopram, Citalopram, Paroxetine)	Selectively inhibit presynaptic 5-HT reuptake transporter (SERT), increasing synaptic serotonin	First-line for MDD, GAD, Panic Disorder, OCD, PTSD, Social Anxiety, Bulimia Nervosa, PMDD	Sexual dysfunction (anorgasmia, decreased libido — mediated by 5-HT2 receptors), GI distress, SIADH (hyponatremia in elderly), platelet dysfunction/GI bleed, QTc prolongation (citalopram); Paroxetine is most anticholinergic/teratogenic; Fluoxetine has longest half-life
SNRIs (Venlafaxine, Duloxetine, Desvenlafaxine, Milnacipran)	Inhibit both 5-HT and Norepinephrine reuptake transporters (SERT and NET)	MDD, GAD, Diabetic Peripheral Neuropathy, Fibromyalgia, Chronic Musculoskeletal/OA Pain, Stress Urinary Incontinence (duloxetine)	Dose-dependent Hypertension (sympathetic NE stimulation — monitor BP with venlafaxine!), diaphoresis, sexual dysfunction, severe discontinuation syndrome if stopped abruptly
NDRI (Bupropion)	Inhibits Norepinephrine and Dopamine reuptake (NET and DAT); nicotinic ACh receptor antagonist	MDD (especially with fatigue/hypersomnia), Seasonal Affective Disorder, Smoking Cessation, SSRI-induced sexual dysfunction adjunct	Zero sexual dysfunction and no weight gain; lowers seizure threshold -> strictly contraindicated in Seizure disorders, Anorexia/Bulimia Nervosa, and acute alcohol withdrawal
Alpha-2 Antagonist (Mirtazapine)	Blocks presynaptic alpha-2 adrenergic autoreceptors and heteroreceptors (increasing NE and 5-HT release) + potent 5-HT2, 5-HT3, and H1 antagonist	MDD in elderly or cachectic/cancer patients with severe insomnia, anorexia, or chemotherapy-induced nausea	Marked sedation (interestingly more sedating at lower doses due to H1 predominance) and increased appetite/weight gain; minimal sexual side effects
Serotonin Modulator (Trazodone)	5-HT2A/2C antagonist, weak SERT inhibitor, and potent alpha-1 and H1 antagonist	Refractory Insomnia (used at low doses 25–100 mg); rarely used at high antidepressant doses due to sedation	Orthostatic hypotension (alpha-1 blockade), heavy sedation, and Priapism ('TrazoBONE' — ischemic veno-occlusive priapism >4 hr requires intracavernosal phenylephrine and corporal aspiration)
Tricyclic Antidepressants (Amitriptyline, Nortriptyline, Imipramine, Clomipramine)	Inhibit 5-HT and NE reuptake + block Muscarinic M1, Histamine H1, Alpha-1, and Cardiac Fast Na+ channels	Neuropathic pain, Migraine prophylaxis (amitriptyline), OCD (clomipramine), Nocturnal Enuresis (imipramine)	Tri-C's of TCA overdose: Convulsions, Coma, Cardiotoxicity (QRS prolongation >100 ms and ventricular arrhythmias via fast Na+ channel blockade -> treat immediately with IV Sodium Bicarbonate!)
MAO Inhibitors (Phenelzine, Tranylcypromine, Isocarboxazid, Selegiline)	Irreversibly or reversibly inhibit Monoamine Oxidase A (degrades 5-HT, NE, tyramine) and MAO-B (degrades dopamine)	Refractory MDD and Atypical Depression (mood reactivity, leaden paralysis, hypersomnia/hyperphagia)	Tyramine Hypertensive Crisis after ingesting aged cheese, cured meats, red wine, or fava beans (GI MAO-A inhibition allows tyramine to enter circulation and displace vesicular NE -> treat with Phentolamine); Serotonin syndrome with SSRIs/meperidine/dextromethorphan

Pharmacologic diagram of monoamine reuptake transporters, presynaptic alpha-2 autoreceptors, and toxicities across antidepressant classes — **Antidepressant Synaptic Targets & Toxicity Mechanisms:** Comparative receptor binding across SSRIs, SNRIs, NDRIs (Bupropion), Alpha-2 antagonists (Mirtazapine), Serotonin modulators (Trazodone, Vilazodone, Vortioxetine), TCAs, and MAOIs. View Full Resolution

Melancholic Depression, Persistent Depressive Disorder (Dysthymia) & Grief vs. MDD

Unlike atypical depression, MDD with Melancholic Features is characterized by profound, unremitting anhedonia and lack of mood reactivity even to joyful events, accompanied by depression that is worse in the morning, early-morning awakening (at least 2 hours before usual), marked psychomotor retardation or agitation, significant anorexia/weight loss, and excessive guilt. Persistent Depressive Disorder (Dysthymia) requires a chronically depressed mood on more days than not for ≥2 years (≥1 year in children/adolescents) with no symptom-free period exceeding 2 consecutive months, plus at least 2 of 6 symptoms (poor appetite/overeating, insomnia/hypersomnia, low energy, low self-esteem, poor concentration, hopelessness). Finally, Normal Bereavement (Uncomplicated Grief) following the loss of a loved one features waves ('pangs') of sadness triggered by reminders of the deceased with preserved self-esteem and ability to experience moments of warmth/humor, whereas MDD features pervasive, unremitting worthlessness, psychomotor retardation, and active suicidal ideation unrelated to joining the deceased.

Antidepressant Response Timeline, Switching Rules & Electroconvulsive Therapy (ECT)

All monoaminergic antidepressants require 4 to 6 weeks at a therapeutic dose to achieve full clinical remission (though sleep and appetite often improve within 1–2 weeks, creating a paradoxical window of increased energy while depressed mood persists). If a patient shows zero response after 4–6 weeks at a maximally tolerated SSRI dose, switch to another SSRI, an SNRI, bupropion, or mirtazapine; if partial response occurs, augment with bupropion, aripiprazole, lithium, or thyroid hormone (T₃). Electroconvulsive Therapy (ECT)—delivered under brief general anesthesia (methohexital) and neuromuscular blockade (succinylcholine)—is the gold-standard, fastest, and most effective treatment for refractory MDD, MDD with severe psychotic features, acute suicidal crisis, refusal to eat/drink causing life-threatening malnutrition, catatonia (refractory to lorazepam), and severe depression/mania in pregnancy; its sole common adverse effect is transient retrograde and anterograde amnesia.

Tricyclic Antidepressant (TCA) Cardiotoxicity & Sodium Bicarbonate Antidote

In intentional overdose, Tricyclic Antidepressants (amitriptyline, nortriptyline, imipramine, doxepin) are the most lethal antidepressant class. Their toxicity stems from four concurrent mechanisms: (1) central anticholinergic and antihistaminic blockade causing delirium, mydriasis, dry flushed skin, urinary retention, and coma; (2) GABA_A receptor antagonism provoking generalized tonic-clonic seizures; (3) peripheral alpha₁-adrenergic blockade causing refractory hypotension; and (4) Vaughan-Williams Class IA-like blockade of cardiac fast voltage-gated Na⁺ channels in the His-Purkinje system and ventricular myocardium, which slows Phase 0 depolarization, widens the QRS complex (>100 ms), produces a prominent terminal R wave (>3 mm) in lead aVR, and triggers fatal ventricular tachycardia or fibrillation. Immediate administration of hypertonic Intravenous Sodium Bicarbonate (NaHCO₃) is mandatory whenever QRS exceeds 100 ms: the high extracellular Na⁺ load overcomes competitive Na⁺ channel blockade, while serum alkalinization (target pH 7.45–7.55) favors the non-ionized form of the TCA and enhances its protein binding.

COMLEX / OMM Integration NBOME High-Yield Correlate

Neuropsychiatric Autonomic Regulation, Cranial Strain & Somatic Viscerosomatics

Psychiatric disorders and psychotropic toxicities exhibit profound autonomic nervous system dysregulation that directly manifests in the musculoskeletal system. Sympathetic hyperactivity during acute panic attacks, mania, catatonia, or serotonin/anticholinergic toxidromes originates along the thoracolumbar chain (T1–L2), with T1–T4 driving tachycardia, pupillary mydriasis, and diaphoresis, and T5–L2 suppressing gastrointestinal peristalsis. Parasympathetic counter-regulation is mediated primarily by the vagus nerve (CN X) exiting the jugular foramen between the temporal and occipital bones, alongside sacral parasympathetics (S2–S4). Patients with Major Depressive Disorder, Generalized Anxiety Disorder, or PTSD frequently harbor somatic dysfunction at the occipitoatlantal (OA) joint, cervical spine (C1–C3), and sphenobasilar synchondrosis (SBS), coupled with hypertonicity of the thoracoabdominal diaphragm and suboccipital musculature. High-yield osteopathic techniques to downregulate sympathetic tone and enhance vagal heart-rate variability include suboccipital inhibition (OA decompression), Compression of the Fourth Ventricle (CV4) (which promotes parasympathetic tone, autonomic quiescence, and cerebrospinal fluid fluctuation), rib raising (T1–T12), and celiac/superior mesenteric/inferior mesenteric ganglion inhibition. In patients developing antipsychotic-induced acute cervical dystonia (spasmodic torticollis) or neuroleptic malignant syndrome ('lead-pipe' rigidity), cervical HVLA is strictly contraindicated; parenteral benztropine or dantrolene must precede gentle indirect myofascial or counterstrain release.

Board Traps & Common Distractors

Never initiate antidepressant monotherapy (SSRIs, SNRIs, TCAs) in a patient with Bipolar I or Bipolar II depression; unopposed serotonergic/noradrenergic stimulation precipitates acute mania, mixed features, rapid cycling, and heightened suicidality.
Clozapine is the most effective antipsychotic for treatment-resistant schizophrenia (failed ≥2 trials) and suicidality, but carries mandatory REMS absolute neutrophil count (ANC) monitoring due to risk of fatal agranulocytosis (discontinue immediately if ANC <1,000/mm³), alongside myocarditis, sialorrhea, and dose-dependent generalized seizures.
Lithium has an extremely narrow therapeutic index (0.6–1.2 mEq/L); concurrent initiation of Thiazide diuretics, NSAIDs (except aspirin), or ACE inhibitors/ARBs reduces renal proximal tubular clearance of lithium and precipitates acute lithium toxicity (coarse tremor, ataxia, confusion, dysarthria, and nephrogenic diabetes insipidus).
Bupropion is strictly contraindicated in patients with a history of seizure disorders, traumatic brain injury, alcohol/benzodiazepine withdrawal, or active eating disorders (Anorexia Nervosa or Bulimia Nervosa), as electrolyte derangements paired with bupropion provoke generalized tonic-clonic seizures.
Allow a mandatory 2-week washout period when switching between an MAOI (phenelzine, tranylcypromine, isocarboxazid, selegiline) and any SSRI/SNRI/TCA—and a 5-week washout when discontinuing Fluoxetine due to its long-acting metabolite norfluoxetine—to prevent fatal Serotonin Syndrome.
In Tardive Dyskinesia (choreoathetoid orofacial lip-smacking, grimacing, and tongue protrusion after chronic D2 blockade), anticholinergics like benztropine WORSEN abnormal movements; treat by tapering the offending antipsychotic (or switching to clozapine/quetiapine) and initiating a VMAT2 inhibitor (valbenazine or deutetrabenazine).
Lamotrigine must be titrated slowly over several weeks (and its dose halved if co-administered with valproate, which inhibits glucuronidation); rapid titration precipitates life-threatening Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN).

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