You’re doing a Q-bank and the stem feels straightforward—until the answer choices are all antidepressants. This is where Step questions live: they’re not just testing if you recognize depression; they’re testing whether you can match clinical context + contraindications + classic side effects + time course to the right class, while actively ruling out the wrong ones.
Tag: Psychiatry > Psychotic & Mood Disorders
The Clinical Vignette (Q-bank style)
A 28-year-old woman comes to clinic for “low mood” for the past 2 months. She reports anhedonia, low energy, impaired concentration, and early-morning awakening. She denies suicidal ideation. She also has recurrent panic attacks and avoids crowded places. Past medical history is notable for bulimia nervosa in remission. She takes no medications. Vitals are normal. Mental status exam shows a depressed mood and anxious affect; no psychosis or mania.
She is started on a medication that is effective for major depressive disorder and panic disorder and is relatively safe in overdose. Two weeks later, she reports mild nausea and feeling “a little more on edge,” but she is functioning.
Which medication is the best choice?
A. Amitriptyline
B. Bupropion
C. Fluoxetine
D. Phenelzine
E. Venlafaxine
Correct Answer: C. Fluoxetine (SSRI)
Why fluoxetine fits the stem
This patient has MDD + panic disorder, and SSRIs are first-line for both. Fluoxetine is also classic for comorbid eating disorders and is generally safe in overdose compared with TCAs and MAOIs.
High-yield SSRI facts (Step-ready)
- First-line for:
- Major depressive disorder
- Panic disorder, GAD, social anxiety
- PTSD
- OCD (often higher doses)
- PMDD
- Time course
- Some side effects early (GI upset, jitteriness)
- Mood/anxiety benefits usually take 2–6+ weeks
- Common adverse effects
- GI upset, headache
- Sexual dysfunction (decreased libido, delayed orgasm)
- Initial activation/anxiety (often transient)
- Insomnia (fluoxetine can be activating)
- Serious
- Serotonin syndrome (esp. with MAOIs, linezolid, triptans, fentanyl, meperidine, dextromethorphan)
- SIADH/hyponatremia (older adults)
- Increased bleeding risk with NSAIDs/anticoagulants
- Pearl: Fluoxetine has a long half-life → fewer withdrawal symptoms, but longer washout needed before MAOI.
Why Every Other Choice Is Wrong (and what they’re testing)
A. Amitriptyline — TCA
TCAs can treat depression and some anxiety symptoms, but they’re not first-line here because they’re dangerous in overdose and have strong anticholinergic/antihistamine effects. Step writers love TCAs as a distractor to see if you recognize their risk profile.
How to spot TCA use cases
- Neuropathic pain (e.g., diabetic neuropathy)
- Migraine prophylaxis
- Depression with prominent insomnia (sedating TCAs like amitriptyline, doxepin)
Key adverse effects (memorize the cluster)
- Antimuscarinic: dry mouth, urinary retention, constipation, blurry vision
- Antihistamine: sedation, weight gain
- blockade: orthostatic hypotension
- Cardiotoxicity (overdose): fast Na channel blockade → wide QRS, ventricular arrhythmias
Overdose treatment
- IV sodium bicarbonate (narrows QRS; treats arrhythmias)
Why it’s wrong in this stem
- Patient is young—overdose safety still matters on exams, and TCAs are a classic “don’t pick unless you must.”
- SSRIs are safer and first-line for panic disorder.
B. Bupropion — NDRI
Bupropion is tempting because it avoids sexual side effects and helps with energy and concentration. But the stem included a very deliberate clue: history of bulimia nervosa.
Absolute exam pearl
- Bupropion is contraindicated in eating disorders (bulimia/anorexia) due to increased seizure risk.
When bupropion is great
- Depression with low energy/fatigue
- Patients concerned about sexual dysfunction
- Smoking cessation
Other high-yield
- Can worsen anxiety early; can cause insomnia
- Side effects: tremor, sweating, weight loss, lowered seizure threshold
Why it’s wrong here
- History of bulimia (even “in remission”) is enough for Step-style avoidance.
D. Phenelzine — MAOI
MAOIs are effective antidepressants and can help with anxiety disorders, but they’re rarely first-line due to serious interactions and dietary restrictions. In Q-banks, they’re usually correct only when the stem screams treatment-resistant depression or atypical depression and you’ve ruled out safer options.
What Step wants you to recall
- Hypertensive crisis with tyramine (“CHEESE reaction”)
- Aged cheeses, cured meats, fermented foods, some wines/beer
- Symptoms: severe headache, diaphoresis, hypertension, possible stroke
- Serotonin syndrome risk with serotonergic drugs
- Requires a washout period:
- Typically 2 weeks between SSRI/SNRI/TCA and MAOI
- 5 weeks for fluoxetine (long half-life)
Why it’s wrong here
- This is a straightforward first-line scenario—MAOI is unnecessarily high risk.
E. Venlafaxine — SNRI
Venlafaxine can be a correct answer in similar stems because SNRIs treat both depression and anxiety disorders. So why isn’t it best here?
What makes SNRIs distinct
- Treat MDD + anxiety disorders (like SSRIs)
- Also helpful for:
- Neuropathic pain
- Fibromyalgia
- Dose-dependent effect
- Lower doses: more serotonergic
- Higher doses: more noradrenergic
High-yield adverse effects
- Similar to SSRIs (GI upset, sexual dysfunction)
- Increased blood pressure (especially venlafaxine at higher doses)
- Discontinuation syndrome can be significant (shorter half-life agents)
Why it’s not the best choice in this stem
- The stem emphasizes safety in overdose and a classic first-line setup; SSRIs are the go-to.
- If the question had uncontrolled hypertension or prominent neuropathic pain, the calculus changes (and venlafaxine might fall out of favor).
One Table to Lock It In
| Class | Examples | Classic uses | Big “testable” adverse effects | Red-flag contraindications / warnings |
|---|---|---|---|---|
| SSRI | Fluoxetine, sertraline, citalopram, escitalopram, paroxetine | MDD, panic, OCD, PTSD, GAD | Sexual dysfunction, GI upset, SIADH; serotonin syndrome | Caution with other serotonergic agents; QT risk (citalopram) |
| SNRI | Venlafaxine, duloxetine | MDD + anxiety; pain syndromes | HTN (venlafaxine), sexual dysfunction, withdrawal | Uncontrolled HTN (relative) |
| TCA | Amitriptyline, nortriptyline, imipramine, clomipramine | MDD (2nd line), neuropathic pain, migraine | Anticholinergic, sedation, orthostasis; wide QRS arrhythmias in overdose | High overdose risk; conduction disease |
| MAOI | Phenelzine, tranylcypromine, selegiline | Atypical or refractory depression | Tyramine hypertensive crisis; serotonin syndrome | Many drug/food interactions; washout required |
| NDRI (common distractor) | Bupropion | Depression, smoking cessation | Seizures, insomnia, anxiety | Bulimia/anorexia, seizure disorder |
Rapid-Fire USMLE Patterns (How Stems Nudge You)
Pick SSRI when you see:
- MDD + anxiety disorder (panic/GAD/social anxiety)
- Need overdose safety
- Comorbid OCD/PTSD
- Young patient, outpatient, uncomplicated presentation
Pick SNRI when you see:
- Depression + chronic pain (neuropathy/fibromyalgia)
- Partial response to SSRI
- But watch for hypertension
Pick TCA when you see:
- Depression is not the main point; instead:
- Neuropathic pain
- Migraine prophylaxis
- Or you’re being tested on toxicity management (wide QRS → bicarb)
Pick MAOI when you see:
- Atypical depression (mood reactivity, hypersomnia, hyperphagia, leaden paralysis)
- Treatment-resistant depression with multiple failed trials
- And the question wants diet/drug interactions
Avoid bupropion when you see:
- Bulimia/anorexia
- Seizure disorder
- Abrupt alcohol/benzo withdrawal
Takeaway: “Why every answer choice matters”
In this vignette, fluoxetine wins because it treats both MDD and panic disorder, fits outpatient first-line practice, and is comparatively safe in overdose. The distractors aren’t random—they each map to a specific Step concept:
- TCA → anticholinergic + lethal overdose (wide QRS; bicarb)
- Bupropion → seizure risk, contraindicated in bulimia/anorexia
- MAOI → tyramine hypertensive crisis + serotonin syndrome + washout
- SNRI → similar efficacy but BP and withdrawal considerations
Mastering these “why not” decisions is what turns antidepressant questions from memorization into pattern recognition.