Patients prescribed any of the 12 most commonly used antidepressants were 21% more likely to experience an episode of weight gain than those not taking the drugs, researchers at King’s College London found.

They also found that the increased relative risk of weight gain hits its peak after two to three years of continued use and that for patients classified as being of ‘normal’ weight, the risk of moving to either the overweight or obese categories increased by 29%, compared to those not taking antidepressants.

For patients in the overweight category, the risk of transitioning to the obese category was also 29% higher for those prescribed antidepressants than those not on the drugs.

Although previous studies have reported short-term weight gain following the start of antidepressant treatment, this study reveals that the risk of weight gain is elevated and sustained for multiple years after the start of treatment.

Calculating Risk

The King’s team analysed the electronic health records of just under 300,000 UK patients — 136,762 men and 157,957 women, from 2004 to 2014.

The group was analysed according to whether or not they had been prescribed an antidepressant in a given year and was made up of patients from all weight categories. These included patients who were classified as being of normal weight (BMI between 18.5 to 24.9), overweight (25.0 -29.9), simple obesity (35.0-34.9), severe obesity (35 -35.9), morbid obesity (40.0 to 44.9) and super obesity (45.0 or greater).

During the ten-year follow-up period, any recorded increase in body weight of at least 5% was identified. Because patients took antidepressants intermittently throughout the ten years, researchers assessed the actual time they were at risk in order to calculate the annual risk for the entire cohort.

[caption id=“attachment_95688” align=“aligncenter” width=“680”]antidepressant weight gain Adjusted rate ratios for ≥5% weight gain by number of years of antidepressant treatment.
Credit: Gafoor Rafael, et al. CC-BY[/caption]

Weight gain was calculated as an increase of 5% of baseline weight; this equates to approximately 7 pounds for a 155 pound person. Researchers also found that that the annual risk of this weight increase was 8.1 per 100 for the group not taking antidepressants, but 11.2 per 100 for those taking antidepressants.

During the second and third years of treatment (the peak risk period) the chance of a 5% body weight gain for those on antidepressants was at least 46% higher than in the group not taking antidepressants. The risk of weight gain remained elevated for up to six years.

Speak To Your Doctor

Speaking about the research, lead author Dr. Rafael Gafoor from King’s College London, said:

“Our results show that antidepressant treatment increases the risk of patients gaining weight over a period of years. From a clinical perspective, these observations reinforce the need for active, tailored and sustained body weight management to go hand in hand with the prescribing of antidepressant treatments. It’s important to stress that no patients should stop taking their medication and that if they have any concerns they should speak with their doctor or pharmacist."

The cohort study offers more insight into the growing global obesity trend, pointing out that antidepressant use is also increasingly widespread. Associations between antidepressant use and subsequent weight gain appear to vary widely within and between antidepressant classes, according the the results.

Therefore, the authors write, risk of weight gain should be considered when antidepressants are to be prescribed.

Support for the study came from NIHR Biomedical Research Centre at Guy’s and St Thomas’ NHS Foundation Trust and King’s College London.

Gafoor Rafael, Booth Helen P, Gulliford Martin C Antidepressant utilisation and incidence of weight gain during 10 years’ follow-up: population based cohort study BMJ 2018; 361 :k1951

Top Image: Steve Snodgrass/Flickr

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