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A new review has found that people who were given certain antidepressant drugs may gain up to 2 kilograms in weight within the first two months of treatment.
The aim of the study was to rank antidepressants according to their known side effects, particularly those emerging within the first eight weeks of starting treatment.
The team, led by experts from the Institute of Psychiatry, Psychology and Neuroscience (IoPPN) at King’s College London, analyzed data from 58,534 participants in more than 150 studies, which compared 30 antidepressants with a dummy drug, known as a placebo.
They found the most noticeable difference in weight change; heart rate And Blood Pressure.
The researchers said patients should be “empowered” by the findings published in The Lancet, but they urged them to talk to a doctor if they have any concerns.
In 2024/25, approximately 92.6 million antidepressants were prescribed to an estimated 8.89 million patients in England.
According to figures from the NHS Business Services Authority (NHSBSA), an estimated 2.9 million patients in England were prescribed the antidepressant sertraline last year.
The drug, also known as Lustral, was associated with a weight loss of 0.76 kilograms and a reduction in heart rate of an average of two beats per minute, but it was also associated with a slight increase in systolic and diastolic blood pressure.
NHSBSA data shows that amitriptyline was prescribed to 2.2 million patients in England in 2024/25.
The drug was associated with an average weight gain of 1.6 kg; There is an increase in heart rate by nine beats per minute as well as an increase in both systolic and diastolic blood pressure.
Amitriptyline is a type of medication called a tricyclic antidepressant. These types of antidepressants are not recommended as first-line treatments for depression because the National Institute for Health and Care Excellence urges physicians to try a type of treatment called selective serotonin reuptake inhibitors (SSRIs) – such as sertraline – first.
As well as being used as a treatment for low mood and depression, amitriptyline may also be prescribed for pain management and migraine.
About 1.4 million people were prescribed citalopram, another SSRI, last year.
Researchers found that the drug was associated with patients losing an average of 0.65 kilograms in weight, and they saw an average reduction in heart rate and systolic blood pressure, but a modest increase in diastolic blood pressure.
Overall, the researchers found that there was “about a 4 kg difference in weight change” depending on which drug patients were given – those given agomelatine lost an average of 2.44 kg, while those given maprotiline – which is not commonly prescribed in the UK – lost an average of 1.82 kg.
On heart rate, they found “a difference of more than 21 beats per minute in heart rate change” between fluvoxamine, which reduced heart rate by eight beats per minute, and nortriptyline, which increased it by an average of 13.8 beats per minute.
Researchers say that every 1 kg weight gain increases the patient’s heart risk.
And increasing blood pressure can increase a person’s risk of stroke.
But he acknowledged that a major limitation of the study was that it focused on the first eight weeks of treatment, and said more research is needed to assess long-term side effects.
“Antidepressants are one of the most widely used medications in the world,” said senior author of the study, Dr Toby Pillinger, a consultant psychiatrist and an academic clinical lecturer at King’s IOPPN.
“While many people benefit from them, these medications are not the same – some can produce meaningful changes in weight, heart rate and blood pressure in a relatively short period of time.
“Our findings show that SSRIs, which are the most commonly prescribed type of antidepressant, have fewer physical side effects, which is reassuring. But for others, closer physical health monitoring may be needed.
“The aim is not to prevent use, but to empower patients and physicians to make informed choices and encourage personalized care.”
Andrea Cipriani, professor of psychiatry at the University of Oxford and study author, said: “Most clinical decisions – particularly in mental health – are still made by physicians with little input from patients.
“Our results emphasize the importance of shared decision making, the collaborative process through which patients are supported by physicians to make decisions about their treatment, bringing together their preferences, personal circumstances, goals, values and beliefs.
“This must be the way forward for the NHS and globally.”
Commenting on the study, Rosie Weatherly, information content manager at mental health charity Mind, said: “It is very important that people get mental health support and treatment that considers their individual needs and preferences.
“As this study highlights, antidepressants vary in their side effects and health professionals need to carefully consider the benefits and risks of different medications for different people.
“If you are already taking medication and you are concerned about its side effects, it is always best to ask your doctor or pharmacist for advice.
“It is important not to stop taking any medicines without advice from a health professional about doing it safely.”
Professor Azeem Majeed, Chair of Primary Care and Public Health at Imperial College London, said: “For patients and clinicians, the results underline the need for regular physical health checks in those treated with antidepressants.
“Furthermore, awareness of these side effects is essential to aid in shared decision making about the risks and benefits of treatment with antidepressants.”