**Question:** A 19 year-old woman is brought to psychiatry outpatient by her boyfriend for depression and suicidal thoughts. Boyfriend reports that patient yesterday expressed extreme sadness and desire to die. The boyfriend reports that they, along with a couple of friends, were partying for the last three days as exams had ended and, on further probing, revealed that they used alcohol and 'other things' too. He further reported that the patient was in great spirits and was enjoying till yesterday, however, subsequently she slept for 20 hours, missed the college and was looking very tired. The patient herself reported that she is feeling very low, and feeling hungry and that she saw very vivid and upsetting dreams during the sleep? Which of the following is the most likely diagnosis in this patient?

A. Depression
B. Postpartum depression
C. Substance-induced mood disorder
D. Hypothyroidism

**Correct Answer:** **C. Substance-induced mood disorder**

In this clinical scenario, the patient presents with symptoms of depression, suicidal ideation, sleep disturbances, and vivid dreams, which are attributed to substance exposure. The patient and her boyfriend both report a history of substance use, specifically during the last three days when they were partying post-exam period. The sudden onset of symptoms after substance use, as well as their resolution upon cessation of substance intake, strongly suggests a substance-induced mood disorder as the most likely diagnosis.

The patient's feelings of sadness, hunger, and vivid dreams during sleep are consistent with the effects of certain substances. Substance-induced mood disorder is a category of psychiatric disorders that occur in response to a substance, typically drugs or alcohol.

The other options are not supported by the provided clinical information:

**A. Depression:** While the patient may indeed be experiencing depression, the specific link to substance exposure is not mentioned, so depression alone cannot be the primary diagnosis.

**B. Postpartum depression:** This diagnosis is specific to women in the postpartum period, which is not mentioned in the scenario.

**D. Hypothyroidism:** Hypothyroidism typically presents with a constellation of symptoms, such as fatigue, weight gain, cold intolerance, and constipation, which are not present in the given scenario.

The core concept here is that the patient developed symptoms following substance exposure and experiences improvement after substance cessation. In this context, the most appropriate diagnosis is **C. Substance-induced mood disorder**.