Diagnosis and Treatment
What you must know
This is the largest clinical domain: DSM-5-TR criteria, differential diagnosis, and evidence-based pharmacologic and somatic treatment across the lifespan. Know criteria and key exclusions for major depressive disorder, bipolar disorders, schizophrenia spectrum, anxiety disorders, OCD, PTSD, ADHD, substance use disorders, and neurocognitive disorders. Know first-line agents, dosing ranges, monitoring, and adverse effects: SSRIs/SNRIs, bupropion (seizure risk), mirtazapine (weight gain, sedation), mood stabilizers (lithium levels and toxicity, lamotrigine rash, valproate hepatotoxicity/teratogenicity), antipsychotics (metabolic monitoring, EPS, NMS, QT), and stimulants/non-stimulants for ADHD. Understand treatment-resistant strategies, augmentation, and when to use ECT, TMS, or ketamine.
Traps
Classic pitfalls: diagnosing MDD without screening for mania (antidepressant-induced switch); missing medical mimics (hypothyroidism, sleep apnea, substance use); ignoring bipolar disorder before starting an antidepressant; failing to order baseline and follow-up metabolic monitoring for antipsychotics; and mismanaging lithium toxicity in dehydration or with NSAIDs/thiazides. Watch for pediatric and geriatric dosing cautions and pregnancy considerations.
Rule of thumb
Before treating depression, always screen for mania and substance use. For lithium, remember the "3 T's"-tremor, thirst, toilet (polyuria)-as early toxicity clues, and check levels after any dehydrating illness or interacting drug.
Worked example: A patient started on an SSRI develops agitation, decreased need for sleep, and rapid speech. Recognize a possible manic switch, stop the antidepressant, and reassess for bipolar disorder rather than increasing the dose or adding a stimulant.