After adjustment for those potential confounders, people prescribed antidepressants were 21% more likely to experience substantial weight gain than those not prescribed them (adjusted rate ratio = 1.21; P less than .001). The researchers, cautioned, however, that residual confounding might have inflated the risk.
Those who had a normal weight when they began taking antidepressants had 29% greater risk of gaining enough weight to meet the criteria for overweight or obesity. Likewise, those already overweight when first prescribed antidepressants were 29% more likely to develop obesity.
For every 27 patients who took antidepressants for at least 1 year, 1 of them gained at least 5% in BMI during the subsequent year. Again, however, the researchers emphasized the absence of evidence for causality and the risk of bias from confounding.
Mirtazapine was the antidepressant associated with the highest incidence ratio of weight gain, but that drug was prescribed infrequently.