Cyproheptadine hydrochloride (Periactin) is used by athletes primarily to:

Cyproheptadine hydrochloride, commonly known as Periactin, is an antihistamine that has the side effect of increasing appetite. Athletes may use it primarily to promote weight gain, especially in situations where they are struggling to maintain or increase their body weight. This can be particularly beneficial for individuals who have a high metabolism or those engaging in intense training regimens that burn a significant amount of calories, making it difficult to achieve the caloric surplus needed for weight gain.

While the other potential uses of cyproheptadine, such as decreasing anxiety or enhancing recovery, may have some relevance in various contexts, they are not the primary reason athletes turn to this medication. Its effectiveness as an appetite stimulant is the primary draw for athletes who want to gain weight and muscle mass. Therefore, the correct choice relates directly to its influence on appetite and subsequent weight increase.