The side effects of different antidepressants have been ranked – revealing a huge difference between drugs.
Researchers looked at the impact medications had on patients in the first eight weeks of starting treatment.
It revealed individuals prescribed certain antidepressants may gain up to 2kg in weight, vary heart rate by as much as 21 beats every minute or have changes in blood pressure.
“Antidepressants are among the most widely used medicines in the world. While many people benefit from them, these drugs are not identical – some can lead to meaningful changes in weight, heart rate, and blood pressure in a relatively short period,” said senior author of the study Dr Toby Pillinger, an academic clinical lecturer at King’s IoPPN, a consultant psychiatrist.
Led by experts from King’s College London’s Institute of Psychiatry, Psychology & Neuroscience (IoPPN), the team analysed data from 58,534 participants across over 150 studies, comparing 30 antidepressants against a dummy drug, known as a placebo.
Researchers said that the findings, which have been published in The Lancet, should “empower” patients but urged them to speak with a medic if they have any concerns.
About 92.6 million antidepressants were prescribed to an estimated 8.89 million patients in England over the past year.
According to data from NHS Business Services Authority (NHSBSA) the antidepressant sertraline was prescribed to an estimated 2.9 million patients in England last year.
This drug, also known as Lustral, was linked to a 0.76kg weight loss and a reduction in heart rate of an average of two beats per minute, but it was also linked to slight increases in systolic and diastolic blood pressure.
NHSBSA data show that amitriptyline was given to 2.2 million patients in England in 2024/25.
This drug was linked to a 1.6kg increase in weight, on average; an increase in heart rate of nine beats per minute as well as increases in both systolic and diastolic blood pressure.
Amitriptyline is a type of drug called a tricyclic antidepressant. This type of antidepressant is not recommended as a first-line treatment for depression as the National Institute for Health and Care Excellence urges medics to try a type of treatment called a selective serotonin reuptake inhibitors (SSRI) – like sertraline – first.
As well as being used as a treatment for low mood and depression, amitriptyline can also be prescribed for pain management and migraine.
Some 1.4 million people were prescribed citalopram last year, another SSRI.
Researchers found this drug was linked to patients losing an average of 0.65kg in weight, and they also, on average, saw decreases to heart rate and systolic blood pressure, but a slight increase in diastolic blood pressure.
Overall, researchers found that there was an “approximate 4kg difference in weight change” depending on which drugs patients were prescribed – with those given agomelatine losing an average of 2.44kg while those given maprotiline – which is not usually prescribed in the UK – putting on an average of 1.82kg.
On heart rate, they found “over 21 beats-per-minute difference 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 point out that each 1kg in weight gain increases a patients’ heart risk.
And increases in blood pressure can increase a person’s risk of stroke.
But they acknowledged that a key limitation of the study was that it focused on the first eight weeks of treatment, and said that further research is needed to assess longer-term side effects.
“Our findings show that SSRIs, which are the most prescribed type of antidepressant, tend to have fewer physical side-effects, which is reassuring. But for others, closer physical health monitoring may be warranted,” said Dr Pillinger.
“The aim isn’t to deter use, but to empower patients and clinicians to make informed choices and to encourage personalised care.”
Study author Andrea Cipriani, professor of psychiatry at the University of Oxford, added: “Most clinical decisions – especially in mental health – are still made by physicians with little input from patients.
“Our results emphasise the importance of shared decision making, the collaborative process through which patients are supported by the clinicians to reach a decision about their treatment, bringing together their preferences, personal circumstances, goals, values and beliefs.
“This should be the way forward in the NHS and globally.”
Commenting on the study, Rosie Weatherly, information content manager at the mental health charity Mind, said: “It’s so important that people receive 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’re already taking medication and you’re worried about its side effects, it’s always OK to ask your doctor or pharmacist for advice.
“It’s important not to stop taking any medication without advice from a health professional about how to do this safely.”
Professor Azeem Majeed, chairman of primary care and public health at Imperial College London, said: “For patients and clinicians, the results underscore the need for routine physical health checks in those treated with antidepressants.
“Moreover, awareness of these side effects is essential to support shared decision-making about the risks and benefits of treatment with antidepressants.”
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