King’s College London and Oxford researchers compared 30 antidepressants for physical impact

The physical side effects of antidepressants have been compared and ranked for the first time, revealing striking differences between commonly prescribed drugs, according to new research.

Scientists from King’s College London and the University of Oxford analysed 151 clinical studies involving more than 58,000 patients taking 30 antidepressants. Their findings, published in The Lancet, show that some medications can cause changes in weight, heart rate and blood pressure significant enough to influence long-term health.

The team examined the impact of the drugs during the first eight weeks of treatment — the period when patients are most likely to experience side effects. They found that, on average, one in six adults in Europe and North America takes some form of antidepressant.

Among the findings, the researchers identified a difference of more than 4kg between the drugs most likely to cause weight loss and those associated with weight gain. Agomelatine was linked to a 2.4kg reduction over eight weeks, while maprotiline caused an average gain of nearly 2kg.

Similarly, heart rate varied by as much as 21 beats per minute between drugs, with fluvoxamine tending to slow the heart and nortriptyline accelerating it. Blood pressure also showed an average difference of 11mmHg between nortriptyline and doxepin.

Professor Oliver Howes, a psychiatrist at King’s College London and one of the study’s authors, said the results underline the importance of tailoring antidepressant prescriptions to individual patients.

“There are big differences between these medicines, and that matters,” he said. “It’s important not just for individual patients but for public health, because even modest effects can add up when large numbers of people are taking them.”

Dr Atheeshaan Arumuham, another co-author, said the research highlighted that “no two antidepressants are built the same”, and that side effects could “stack up in ways that become clinically important”, such as increasing the risk of cardiovascular problems.

The study emphasised that patients should not stop or change their medication without medical advice, but urged doctors to consider physical health impacts when choosing treatments.

Dr Toby Pillinger from King’s College London, who also worked on the analysis, told BBC Radio 4’s Today programme that the data should help patients make more informed choices about their care.

“The last thing I want is for this story to scare people,” he said. “It should be seen as empowering — giving people the confidence to engage in shared decision-making with their practitioners.”

He added that the changes seen within just eight weeks were large enough to be clinically relevant. “Even over that short period, we saw differences that could have real health implications,” he said.

The findings suggest that two patients with the same diagnosis could require different antidepressants depending on their existing conditions or side-effect concerns. Someone prone to weight gain, for example, may be better suited to a drug such as agomelatine, while those with high blood pressure or heart disease might need to avoid medications that raise cardiovascular risk.

The researchers say they hope their rankings will help clinicians and patients better navigate a field that affects millions worldwide. They also called for longer-term studies to understand whether these early physical changes persist or worsen over time.

Experts not involved in the research have welcomed the findings but cautioned that treatment decisions should balance physical effects with how well each drug controls symptoms of depression.