Major Depressive Disorder (MDD) is a depressive disorder in which sad, empty, or irritable mood, plus physical and cognitive changes like sleep, appetite, and concentration problems, persist for at least two weeks and impair daily functioning. It is one of two depressive disorders named in the AP Psychology CED.
Major Depressive Disorder (MDD) is one of the two depressive disorders explicitly in scope for AP Psychology (the other is persistent depressive disorder). The CED defines depressive disorders as conditions involving a sad, empty, or irritable mood along with physical and cognitive changes that affect a person's ability to function. For MDD specifically, that means persistent sadness or hopelessness, loss of interest or pleasure in activities (anhedonia), changes in appetite or sleep, trouble concentrating, and sometimes thoughts of suicide. These symptoms last at least two weeks and genuinely disrupt everyday life. That functional impairment piece matters because feeling down for a few days does not qualify.
The CED also tells you exactly which causal lenses are fair game. Possible causes of depressive disorders are biological, genetic, social, cultural, behavioral, or cognitive. That list is basically the biopsychosocial model in disguise, and the exam loves asking you to explain depression through more than one of those lenses at once. Low serotonin activity is a biological explanation, learned helplessness is a behavioral one, and a negative explanatory style is a cognitive one. Knowing which explanation belongs to which perspective is half the battle.
MDD lives in Unit 5: Mental and Physical Health and directly supports learning objective AP Psych Revised 5.4.C, which asks you to describe the symptoms and possible causes of selected depressive disorders. It also feeds the treatment topics, where you connect a disorder to the therapy designed for it. Biological treatments like antidepressant medication target the brain chemistry side, while psychological treatments like cognitive therapy target the maladaptive thinking side. MDD is the single most useful disorder to know cold because it shows up in symptom-identification questions, perspective-matching questions, and treatment-application questions. If a scenario describes someone who has lost interest in everything for three weeks, you should be able to name the disorder, explain it from multiple perspectives, and propose a matching treatment.
Keep studying AP Psychology Unit 5
Persistent Depressive Disorder (Unit 5)
This is MDD's sibling in the depressive disorders category and the most common mix-up. Think of MDD as a severe storm and persistent depressive disorder as a long gray drizzle. MDD is more intense but episodic, while persistent depressive disorder is milder but lasts much longer.
Bipolar Disorder (Unit 5)
Bipolar I and Bipolar II involve periods of depression that can look identical to MDD, but they also include mania or hypomania. On a question, the presence of even one manic episode rules out MDD. Watch for clues like racing thoughts, inflated self-esteem, or sudden bursts of risky energy.
Treatment of Psychological Disorders (Unit 5)
MDD is the classic test case for matching disorder to treatment. The biological perspective points to antidepressants that affect neurotransmitters like serotonin, while the cognitive perspective points to therapy that restructures negative thought patterns. Scenarios often ask what to do when one approach fails, and the answer is usually to pull from the other perspective.
Biases and Errors in Thinking (Unit 5)
The cognitive explanation for MDD connects directly to how thinking goes wrong. A person with depression often shows a stable, internal, global explanatory style for bad events ('it's me, it's permanent, it ruins everything'). That link between distorted cognition and mood is exactly the kind of cross-topic reasoning the exam rewards.
On multiple choice, MDD usually appears as a scenario. You read about someone with weeks of low mood, lost interest, sleep changes, and concentration problems, then identify the disorder or the perspective being used to explain it. The distractors are almost always persistent depressive disorder, bipolar disorder, or generalized anxiety disorder, so know what separates them. Application questions also push past identification. One practice question asks which psychological intervention works best for someone with MDD who is resistant to medication, and another asks you to build a biopsychosocial intervention plan. That is the move to practice: explain MDD from biological, psychological, and social angles, then match a treatment to each. No released FRQ has used the term verbatim, but MDD fits naturally into AAQ and EBQ prompts about disorder causes and treatment effectiveness.
Both are depressive disorders under LO 5.4.C, and both involve sad, empty, or irritable mood with functional impairment. The difference is severity versus duration. MDD features more severe symptoms lasting at least two weeks, while persistent depressive disorder features milder, chronic symptoms that stretch on much longer. If a question describes someone who has felt 'low-level down' for years rather than hit hard for weeks, the answer is persistent depressive disorder, not MDD.
Major Depressive Disorder involves sad, empty, or irritable mood plus physical and cognitive changes that last at least two weeks and impair daily functioning.
MDD and persistent depressive disorder are the only two depressive disorders named in the AP Psychology CED, and they differ mainly in severity versus duration.
The CED lists biological, genetic, social, cultural, behavioral, and cognitive sources as possible causes, so be ready to explain MDD from more than one perspective.
The presence of any manic or hypomanic episode rules out MDD and points to a bipolar disorder instead.
Treatment questions reward matching the perspective to the intervention, such as antidepressant medication for biological explanations and cognitive therapy for maladaptive thinking.
Functional impairment is part of the definition, so ordinary sadness that does not disrupt daily life does not count as MDD on the exam.
It's a depressive disorder defined by sad, empty, or irritable mood along with physical and cognitive changes, like sleep, appetite, and concentration problems, that last at least two weeks and impair daily functioning. It supports learning objective AP Psych Revised 5.4.C in Unit 5.
No. Ordinary sadness fades and doesn't wreck your ability to function. MDD requires symptoms persisting at least two weeks plus real impairment in daily life, which is why the diagnostic threshold exists. Exam questions often test exactly this distinction.
MDD is more severe but episodic, with symptoms lasting at least two weeks. Persistent depressive disorder is milder but chronic, dragging on for a much longer stretch. Both are in scope for AP Psych under depressive disorders.
The CED lists biological, genetic, social, cultural, behavioral, and cognitive sources. In practice that means things like neurotransmitter activity (biological), learned helplessness (behavioral), and negative explanatory styles (cognitive).
MDD involves only depressive episodes. Bipolar I and Bipolar II add periods of mania or hypomania that alternate with depression. If a scenario mentions racing thoughts, inflated confidence, or risky bursts of energy, the answer is a bipolar disorder, not MDD.