The study aimed to rank antidepressants based on known side effects associated with the drugs during the initial eight weeks of treatment
Mature adult man in cozy interior of bedroom ( taking medication)
Certain antidepressants can lead to a weight gain of up to 2kg (4.5lbs) within the first two months of treatment, while other drugs could result in a weight loss of 2.5kg (5.5lbs), according to a recent review. The study aimed to rank antidepressants based on known side effects associated with the drugs during the initial eight weeks of treatment.
The research was spearheaded by academics from the Institute of Psychiatry, Psychology and Neuroscience (IoPPN) at King’s College London, who analysed data from 58,534 individuals participating in over 150 studies comparing 30 antidepressants with a placebo.
The most significant differences were observed in weight change, heart rate, and blood pressure. The findings, published in The Lancet, are intended to “empower” patients, but researchers have urged those with any concerns to consult a healthcare professional.
In the year 2024/25, an estimated 8.89 million patients in England were prescribed some 92.6 million antidepressants. NHS Business Services Authority (NHSBSA) data reveals that last year, the antidepressant sertraline was prescribed to an estimated 2.9 million patients in England.
This drug, also known as Lustral, was associated with a 0.76kg weight loss and a reduction in heart rate by an average of two beats per minute. However, it was also linked to slight increases in systolic and diastolic blood pressure. NHSBSA data indicates that amitriptyline was prescribed to 2.2 million patients in England in 2024/25.
This medication was associated with an average weight gain of 1.6kg, alongside an elevation in heart rate of nine beats per minute, as well as rises in both systolic and diastolic blood pressure. Amitriptyline belongs to a category of medication known as tricyclic antidepressants.
This class of antidepressant isn’t recommended as an initial treatment option for depression, as the National Institute for Health and Care Excellence advises doctors to first attempt a form of therapy called selective serotonin reuptake inhibitors (SSRIs) – such as sertraline. Beyond its use in treating low mood and depression, amitriptyline may also be prescribed for managing pain and migraines.
Approximately 1.4 million individuals received prescriptions for citalopram last year, another SSRI. The research revealed this medication was connected to patients shedding an average of 0.65kg in weight, whilst also experiencing, on average, reductions in heart rate and systolic blood pressure, though with a modest rise in diastolic blood pressure.
In total, researchers discovered an “approximate 4kg difference in weight change” based on which medications patients received – with those administered agomelatine losing an average of 2.44kg whilst those given maprotiline – which isn’t typically prescribed in the UK – gaining an average of 1.82kg. Regarding heart rate, the researchers noted an “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.
The study highlighted that each 1kg increase in weight heightens a patient’s heart risk. Moreover, rises in blood pressure can escalate a person’s risk of stroke. However, the researchers conceded that a significant limitation of their study was its focus on the initial eight weeks of treatment, stating that additional research is required to evaluate longer-term side effects.
“Antidepressants are among the most widely used medicines in the world,” stated Dr Toby Pillinger, senior author of the study and an academic clinical lecturer at King’s IoPPN, as well as a consultant psychiatrist.
“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. 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.
“The aim isn’t to deter use, but to empower patients and clinicians to make informed choices and to encourage personalised care.”
Andrea Cipriani, professor of psychiatry at the University of Oxford and author of the study, stated: “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.”
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Rosie Weatherly, information content manager at the mental health charity Mind, commenting on the study, 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, commented: “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.”
Dr Lade Smith, president of the Royal College of Psychiatrists, commented: “Antidepressants play a key role in the treatment of more severe depression and are particularly effective when used in combination with talking therapies. As with all drugs, antidepressants have side effects, and we very much welcome this study which helps improve our understanding of some of the physical side effects that can be caused by different types of antidepressants.
“These findings will help patients and clinicians choose the medication that is best suited to their personal needs.”
Professor Kamila Hawthorne, chair of the Royal College of GPs, stated that patients would only be prescribed antidepressants “with good reason”, and GPs would follow up with patients two to three weeks after a new prescription to monitor for side effects.
She further added that patients would be invited for regular medication reviews. “These reviews are particularly important, as this study suggests, given that various factors, including lifestyle, can change how an antidepressant works,” she said.