A BBC expert has raised concerns about a range of commonly prescribed antidepressants which are utilised by eight million people across the UK.
Fresh research published this week has revealed that individuals taking particular antidepressants may gain up to 2kg (4.5lbs) during the initial two months of treatment, whilst patients on alternative medications could lose 2.5kg (5.5lbs).
Researchers aimed to categorise antidepressants according to various recognised side effects associated with the medications within the first eight weeks of commencing treatment.
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The study team, headed by scholars from the Institute of Psychiatry, Psychology and Neuroscience (IoPPN) at King's College London, analysed information from 58,534 individuals who participated in over 150 trials comparing 30 antidepressants against a placebo.
Speaking on BBC Morning Live today, Dr Kasim Ahmed characterised the headlines as 'pretty scary' "if you're one of the 8 million people in the country that uses an antidepressant."
He continued: "The important thing that needs to be mentioned here... is that these medications have been given for a reason and that reason is because of a mood disorder of some kind, whether that's depression, anxiety, bipolar affective disorder.
"These are very, very good medications at solving someone's problems or helping someone deal with some of the problems that they're facing as a result of these mood-based disorders.", reports the Mirror.
The researchers discovered the most significant differences in weight fluctuation, heart rate and blood pressure.
Dr Kasim revealed that the study examined data from 50,000 patients and the effects of medication between 8 - 12 weeks after beginning treatment.
He said: "What we're going to focus on now is the three bigger findings of it, which was weight gain, changes to your blood pressure and changes to the heart rate.
"Essentially what it found is that there's lots of different medications of different classes that can cause changes in your weight as this all starting.
"If we look at weight gain specifically first, some antidepressants, specifically things like amitriptyline, if you're on that is something that we use relatively commonly here, can cause an increase in weight of up to 2 kilogrammes within the 1st 12 weeks of you starting that medication.
"But, however, other antidepressants can cause a big loss in weight as well, so things like sertraline or citalopram can cause a loss in weight up to 1 kilogramme themselves once you've started the medication. But this is a side effect that affects some people, not everyone who's on those medications."
Dr Kasim highlighted the impact on heart rate can cause 'problems'. He stated: "So if you're taking amitriptyline or nortriptyline is a big one, it can cause an increase in your heart rate over the course of 8 to 12 weeks of starting the medication, and sertraline, fluoxetine, so these are the medications which are of a different class, can cause a lowering of your heart rate."
Regarding blood pressure, he explained: "So same classes of drugs, amitriptyline, nortriptyline can cause an increase in your blood pressure, not a massive increase by about 10 points over, an average period of time, and similarly. Sertraline fluoxetine citalopram, which are a class within themselves, can cause a dropping of your blood pressure."
In the year 2024/25, a staggering 92.6 million antidepressants were prescribed to an estimated 8.89 million patients in England. 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 reveal that amitriptyline was given to 2.2 million patients in England in 2024/25.
This medication was associated with a 1.6kg weight gain, on average; a rise in heart rate of nine beats per minute as well as elevations in both systolic and diastolic blood pressure.
Amitriptyline belongs to a class of medication known as a tricyclic antidepressant.
This category of antidepressant isn't advised as a first-line treatment for depression as the National Institute for Health and Care Excellence encourages doctors to attempt a form of treatment called selective serotonin reuptake inhibitors (SSRI) - such as sertraline - initially.
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, said: "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, assured that patients will only be prescribed antidepressants "with good reason". She added that GPs would follow up with patients two to three weeks after a new prescription to monitor for side effects.
She further stated that patients will 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 explained.