To evaluate the long term association between antidepressant prescribing and body weight.Design
Population based cohort study.Setting
General practices contributing to the UK Clinical Practice Research Datalink, 2004-14.Participants
136 762 men and 157 957 women with three or more records for body mass index (BMI).Main outcome measures
The main outcomes were antidepressant prescribing, incidence of ≥5% increase in body weight, and transition to overweight or obesity. Adjusted rate ratios were estimated from a Poisson model adjusting for age, sex, depression recording, comorbidity, coprescribing of antiepileptics or antipsychotics, deprivation, smoking, and advice on diet.Results
In the year of study entry, 17 803 (13.0%) men and 35 307 (22.4%) women with a mean age of 51.5 years (SD 16.6 years) were prescribed antidepressants. During 1 836 452 person years of follow-up, the incidence of new episodes of ≥5 weight gain in participants not prescribed antidepressants was 8.1 per 100 person years and in participants prescribed antidepressants was 11.2 per 100 person years (adjusted rate ratio 1.21, 95% confidence interval 1.19 to 1.22, P<0.001). The risk of weight gain remained increased during at least six years of follow-up. In the second year of treatment the number of participants treated with antidepressants for one year for one additional episode of ≥5% weight gain was 27 (95% confidence interval 25 to 29). In people who were initially of normal weight, the adjusted rate ratio for transition to overweight or obesity was 1.29 (1.25 to 1.34); in people who were initially overweight, the adjusted rate ratio for transition to obesity was 1.29 (1.25 to 1.33). Associations may not be causal, and residual confounding might contribute to overestimation of associations.Conclusion
Widespread utilisation of antidepressants may be contributing to long term increased risk of weight gain at population level. The potential for weight gain should be considered when antidepressant treatment is indicated.