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Weight gain: drug treatment may be the cause

Drugs can sometimes disrupt one or several weight-regulation factors. Psychotropic drugs are most often implicated.

Weight gain is linked to increases in body fat or muscle mass or to fluid retention. The appetite and metabolism regulatory mechanisms are complex and involve a number of hormonal, neuronal and genetic as well as psychological and cultural factors. Disruption of these factors is likely to lead to weight gain.

There are various causes of weight gain (diet, some illnesses, smoking cessation). Weight gain can also be linked to drug treatments.

Drugs that cause weight gain act in different ways: increasing appetite, increasing the craving for sugar, increasing thirst, slowing down of the metabolism, modification of the distribution of fat, reduced physical activity. Of the medicinal treatments causing weight gain, psychotropic drugs are the most frequent (in particular venlafaxine, mirtazapine (antidepressants), olanzapine and clozapine (neuroleptics)). Other drugs include sex hormones and related drugs, diabetes treatments, corticosteroids, antihistamines.

In overweight patients, drugs known to expose the patient to weight gain should be avoided. When one of these drugs is prescribed or dispensed, the patient should be informed of this potential effect. When weight gain is noted, the harm-benefit balance of the drug concerned should be re-evaluated in each case. Halting the treatment generally results in weight loss, but does not always enable the patient to return to their former weight.

©Prescrire 1 January 2012

"Drug-induced weight gain" Prescrire Int 2012; 21 (123): 11-14. (pdf, subscribers only)