Step 1 topics → Psychiatry → Major Depressive Disorder (MDD)

Major Depressive Disorder (MDD)

USMLE Step 1 trap: Confuses 'at least one of depressed mood or anhedonia' with requiring both as mandatory anchors. MDD requires 5 of 9 symptoms for ≥2 weeks, with at least one being depressed mood OR anhedonia (not necessarily both).

Major Depressive Disorder is one of the highest-yield psychiatry topics on USMLE Step 1, and it shows up in more ways than students expect. The exam doesn't just ask you to recite DSM-5 criteria — it gives you a vignette where a patient almost meets criteria, or meets criteria but has a feature that changes management entirely. You need to know the rules cold: 5 of 9 SIGECAPS symptoms for at least 2 weeks, with depressed mood OR anhedonia (not both required) serving as the anchor symptom. The exam also loves to test whether you know when standard antidepressant therapy isn't enough.

The trickiest angles involve distinguishing MDD with psychotic features from schizoaffective disorder, and knowing when depression has become treatment-resistant. These are classic exam setups where one word in the vignette — whether the psychosis occurs only during the mood episode or persists independently — completely changes your answer. Students who haven't thought through the logic of these distinctions will pick the wrong diagnosis or the wrong next step every time.

Psychotherapy (especially CBT) is a legitimate first-line option that the USMLE Step 1 expects you to recognize alongside SSRIs/SNRIs. Don't dismiss it as a soft answer. The exam also expects you to know that treatment-resistant depression requires failure of at least two adequate trials before escalating to options like augmentation with lithium, atypical antipsychotics, or ECT — not just one failed SSRI.

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Common misconceptions

Common mistake
Wrong: MDD requires 5 symptoms including depressed mood AND anhedonia simultaneously.
Right: MDD requires 5 of 9 symptoms for ≥2 weeks, with at least one being depressed mood OR anhedonia (not necessarily both).
The DSM-5 rule is 'at least one of depressed mood OR anhedonia' — either one qualifies as the anchor, and you only need one. The other 4 symptoms can come from anywhere in the remaining SIGECAPS list. Students who think both depressed mood AND anhedonia are simultaneously required will misdiagnose patients who present with anhedonia alone as the primary complaint, which is actually very common in older adults.
Common mistake
Wrong: MDD with psychotic features is treated with an antidepressant alone.
Right: MDD with psychotic features requires an antidepressant plus an antipsychotic, or ECT.
An antidepressant alone won't touch the psychotic symptoms, which require dopamine blockade. The correct treatment is combination therapy — an antidepressant plus an antipsychotic — or ECT, which works well for both components simultaneously. Giving only an antidepressant to someone with MDD with psychotic features is an incomplete and potentially dangerous plan that the exam will penalize.
Common mistake
Wrong: Treatment-resistant depression is defined as failure of one adequate antidepressant trial.
Right: Treatment-resistant depression is defined as failure of at least two adequate antidepressant trials of different classes at therapeutic doses for sufficient duration.
One failed trial just means you need to try a different antidepressant, possibly from a different class or at an adequate dose and duration. Treatment-resistant depression is a specific label requiring at least two adequate trials — adequate meaning therapeutic dose, sufficient duration (typically 4-8 weeks), from different medication classes. Jumping to ECT or augmentation after one failed trial is premature and wrong on USMLE Step 1.
Common mistake
Wrong: Psychotic symptoms occurring only during depressive episodes indicate schizoaffective disorder.
Right: Psychotic symptoms confined exclusively to mood episodes indicate MDD with psychotic features, not schizoaffective disorder, which requires psychosis independent of mood episodes.
The key differentiator is timing of psychosis relative to mood episodes. In MDD with psychotic features, hallucinations or delusions occur exclusively during depressive episodes — no mood episode, no psychosis. In schizoaffective disorder, psychosis persists independently of mood episodes, meaning the patient has psychotic symptoms even when not depressed. If the vignette describes psychosis only during depressive episodes, that's MDD with psychotic features, full stop.
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What the exam tests

  1. Know the DSM-5 criteria precisely: 5 of 9 SIGECAPS symptoms lasting at least 2 weeks, with depressed mood or anhedonia (either one, not both) as a required anchor symptom.
  2. Identify first-line treatment for MDD — SSRIs are the pharmacologic default, but psychotherapy (especially CBT) is equally valid as first-line, and the exam will test whether you recognize this.
  3. Distinguish MDD with psychotic features from schizoaffective disorder depressive type based on whether psychosis occurs only during mood episodes (MDD with psychosis) or also independently of them (schizoaffective), and know that MDD with psychosis requires antidepressant plus antipsychotic or ECT.
  4. Define treatment-resistant depression correctly as failure of at least two adequate antidepressant trials from different classes at therapeutic doses, and recognize the next-step options including augmentation or ECT.

Can you avoid these mistakes?

A 34-year-old woman reports 3 weeks of low energy, hypersomnia, weight gain, difficulty concentrating, and loss of interest in activities she used to enjoy. She denies feeling sad and says her mood feels 'flat.' Does she meet criteria for MDD, and why or why not?
A patient with MDD is started on sertraline at a therapeutic dose. After 6 weeks he has minimal improvement, so his psychiatrist switches him to venlafaxine. After another 6 weeks there is still no adequate response. What is the correct label for this patient's condition, and what are appropriate next-step options?
A 45-year-old man presents with a 3-week depressive episode during which he hears voices telling him he is worthless. A thorough history confirms he has never experienced psychotic symptoms outside of his depressive episodes. What is the diagnosis, and what is the correct pharmacologic treatment?
A vignette describes a patient with depressed mood, anhedonia, insomnia, fatigue, and feelings of worthlessness for the past 3 weeks — exactly 5 symptoms. Her psychiatrist diagnoses MDD and recommends treatment. A classmate says you need 5 symptoms plus depressed mood AND anhedonia to diagnose MDD. Who is correct, and why?

Related topics

Persistent Depressive Disorder (Dysthymia) Bipolar I Disorder Bipolar II Disorder Cyclothymic Disorder

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