## Core Concept
Weight gain as a side effect is commonly associated with several medications, particularly those used in psychiatry and for certain chronic conditions. The underlying reasons include increased appetite, altered metabolism, or changes in fat distribution. Understanding which medications cause weight gain is crucial for managing patients, especially those with or at risk of obesity-related conditions.

## Why the Correct Answer is Right
Prinzmetal's angina, also known as variant angina, is caused by transient coronary artery spasm. The treatment often involves calcium channel blockers, nitrates, and sometimes other classes of drugs. Weight gain is not a commonly associated side effect of the primary treatments for Prinzmetal's angina. In contrast, many psychiatric medications and some drugs for diabetes and hypertension can lead to weight gain.

## Why Each Wrong Option is Incorrect
* **Option A:** Certain antipsychotics, especially the second-generation (atypical) antipsychotics like olanzapine and clozapine, are well-known to cause significant weight gain. This is due to their effect on various neurotransmitter systems that regulate appetite and metabolism.
* **Option B:** Some antidepressants, particularly certain selective serotonin reuptake inhibitors (SSRIs) like paroxetine and fluoxetine (though less commonly with the latter), and especially some tricyclic antidepressants, can cause weight gain. The mechanism may involve changes in appetite and possibly alterations in serotonin and other neurotransmitter functions.
* **Option D:** Corticosteroids are known to cause weight gain through various mechanisms, including increased appetite, fluid retention, and changes in fat distribution (e.g., moon facies, buffalo hump). This side effect is a significant concern with long-term use.

## Clinical Pearl / High-Yield Fact
A key point to remember is that when managing patients on medications known to cause weight gain, monitoring weight regularly and discussing lifestyle modifications (diet and exercise) can help mitigate this side effect. For some medications, switching to a different agent with a more favorable side effect profile regarding weight may be necessary.

## Correct Answer: C.