Drug-induced weight loss is the involuntary loss of body weight as an attributable side effect of a particular medication or substance of abuse. The etiology for weight loss varies depending on the medication. Some medications increase the underlying metabolic rate (either directly or through hormonal effects) resulting in weight loss, while other medications cause anorexia, nausea, dyspepsia, or dysgeusia, all of which can result in weight loss from decreased caloric intake. Patients abusing stimulant medications such as cocaine or amphetamines often experience weight loss. Alcohol use disorder is often associated with malnutrition and subsequent weight loss.

Medications associated with weight loss include antibiotics, acetylcholinesterase inhibitors, sedatives, serotonin reuptake inhibitors, antiretrovirals, anticonvulsants, antifungals, antidiabetics, tyrosine kinase inhibitors, monoclonal antibodies, and alkylating agents.

Weight loss as an adverse effect from a medication can occur slowly, often over a period of several months. It is important for physicians to monitor their patients closely after initiating treatment with medications placing patients at risk for unintentional weight loss with surveillance office visits, as early recognition is the ideal management strategy. Often through dose adjustments, medication changes, or nutrition consultation, the downstream sequelae of malnutrition can be averted.