Which hypnotic medication may potentially increase body weight?

Diphenhydramine is an antihistamine commonly used as a hypnotic medication due to its sedative properties. One of the known side effects of diphenhydramine is weight gain, which can be attributed to several factors.

First, diphenhydramine can increase appetite, leading individuals to consume more calories than they would otherwise. Second, the sedative effects may cause individuals to be less active, contributing to an overall decrease in energy expenditure.

While sertraline is an antidepressant that can have varying effects on weight (it may contribute to either weight loss or weight gain depending on the individual), alprazolam, a benzodiazepine, is typically not associated with significant weight changes. Melatonin, a hormone that regulates sleep-wake cycles, has not been linked to weight gain and is generally considered weight-neutral. Therefore, among the options presented, diphenhydramine is the medication most associated with an increase in body weight due to its appetite-stimulating and sedative effects.