## **Core Concept**
The diagnosis of major depressive disorder (MDD) is based on the presence of depressed mood or loss of interest in activities for a specified duration, along with other diagnostic criteria. The **Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5)** provides standardized criteria for psychiatric diagnoses.

## **Why the Correct Answer is Right**
To classify someone as suffering from major depressive disorder (MDD), the DSM-5 requires that the depressive symptoms persist for at least **2 weeks**. This duration criterion helps distinguish MDD from transient or normal reactions to stressful life events. The symptoms must cause significant distress or impairment in social, occupational, or other areas of functioning.

## **Why Each Wrong Option is Incorrect**
* **Option A (1 week):** This duration is too short for the diagnosis of MDD according to the DSM-5. Some diagnostic criteria may require a shorter duration for other conditions, but for MDD, 2 weeks is the threshold.
* **Option C (3 weeks):** While a longer duration might ensure that the condition is not transient, the DSM-5 specifically sets the threshold at 2 weeks, making 3 weeks more than required.
* **Option D (4 weeks):** Similar to option C, this is longer than the required duration for a diagnosis of MDD.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the diagnosis of major depressive disorder requires a minimum duration of **2 weeks** of depressed mood or loss of interest, along with at least five of the other specified symptoms. This helps in distinguishing MDD from normal grief or transient sadness.

## **Correct Answer:** B. 2 weeks.