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A new review finds that people starting certain antidepressants may gain up to 2kg (4.5lbs) in the first two months, while others could lose around 2.5kg (5.5lbs). Researchers aimed to rank antidepressants according to various known side effects observed during the first eight weeks of treatment. The study, conducted by researchers from the Institute of Psychiatry, Psychology & Neuroscience (IoPPN) at King's College London , analysed data from 58,534 participants across more than 150 studies that compared 30 different antidepressants with a dummy drug, known as a placebo. The researchers observed the most significant differences in weight changes, heart rate and blood pressure . Published in The Lancet, the study's authors said the findings should "empower" patients, while also advising them to consult a doctor if they have any concerns, the Mirror reports. In 2024/25, around 92.6 million antidepressant prescriptions were issued to an estimated 8.89 million patients in England. NHS Business Services Authority (NHSBSA) data indicate that sertraline, also known as Lustral, was prescribed to roughly 2.9 million patients last year. Sertraline was associated with an average weight loss of 0.76kg and a reduction in heart rate of about two beats per minute, though it also showed slight increases in both systolic and diastolic blood pressure. The NHSBSA data also reveal that amitriptyline was prescribed to 2.2 million patients in England during the same period. Amitriptyline was associated with an average weight gain of 1.6kg, an increase in heart rate of nine beats per minute, and rises in both systolic and diastolic blood pressure. It belongs to a class of medications known as tricyclic antidepressants. These are generally not recommended as a first-line treatment for depression, as the National Institute for Health and Care Excellence (NICE) advises doctors to try selective serotonin reuptake inhibitors (SSRIs), such as sertraline, initially. In addition to treating low mood and depression, amitriptyline is sometimes prescribed for pain relief and migraine prevention. Last year, around 1.4 million people in England were prescribed citalopram, another SSRI. Researchers found that citalopram was associated with an average weight loss of 0.65kg. Patients also experienced, on average, reductions in heart rate and systolic blood pressure, along with 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 to people in the UK, putting on an average of 1.82kg. Regarding heart rate, the researchers found an "over 21 beats-per-minute difference in heart rate change" between fluvoxamine, which lowered heart rate by eight beats per minute, and nortriptyline, which raised it by an average of 13.8 beats per minute. They also noted that each 1kg of weight gain can increase a patient's risk of heart problems. Elevated blood pressure can also raise a person’s risk of stroke. However, the researchers noted a key limitation of the study: it only examined the first eight weeks of treatment. They emphasised that further research is needed to understand the longer-term side effects of these medications. Senior author of the study Dr Toby Pillinger, an academic clinical lecturer at King's loPPPN and consultant psychiatrist, stated: "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. 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." While study author Andrea Cipriani, professor of psychiatry at the University of Oxford, 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.” Regarding the study, Rosie Weatherly, information content manager at the mental health charity Mind, expressed: "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.” Dr Lade Smith, president of the Royal College of Psychiatrists, added: "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 are prescribed antidepressants "with good reason" and explained that GPs typically follow up with patients two to three weeks after starting a new prescription to monitor for side effects. After this patients will be invited for regular medication reviews, she added. "These reviews are particularly important, as this study suggests, given that various factors, including lifestyle, can change how an antidepressant works,” she said.
