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Weight loss and diabetes jabs such as Mounjaro, Ozempic and Wegovy increase the odds of going bald by up to 68 per cent, a study suggests.
Hundreds of users have been reporting hair loss to regulators in the United States and UK but new research on 50,000 people now appears to firm up the link.
Experts used electronic patient data from the University of Pennsylvania Health System to compare rates of alopecia hair loss in adults using GLP-1s to manage diabetes with those on other drugs.
The team noted that regulators in the US have been informed of the link between the drugs and hair loss, particularly for semaglutide (the active ingredient in Wegovy and Ozempic) and tirzepatide (the active ingredient in Mounjaro).
So far in 2026, the UK Medicines and Healthcare products Regulatory Agency (MHRA) has received 399 reports of hair loss relating to tirzepatide, alongside 541 last year.
It has also received 148 reports of hair loss linked to semaglutide, alongside 164 reports last year.
For the new study, the team looked at people with type 2 diabetes on GLP-1 receptor agonists or other types of diabetes drugs known as SGLT-2 inhibitors, or DPP-4 inhibitors.
In total, 12,004 patients using GLP-1s were compared with 15,221 using SGLT-2 inhibitors and a further 11,964 GLP-1 users were compared with 11,233 DPP-4 inhibitor users.
After adjusting for factors that could influence the results, such as age and weight, researchers found using GLP-1 drugs were associated with a 37 per cent higher risk of alopecia than use of SGLT-2 inhibitors.
GLP-1s were also linked to a 68 per cent higher risk of hair loss than use of DPP-4 inhibitors, according to findings published in The British Medical Journal (BMJ).
Further analysis suggested the link related to non-scarring alopecia, where hair follicles remain intact, leaving the potential for hair to regrow.
The researchers, including from the University of Pennsylvania in the US, wrote: 'Case reports and analyses of the US Food and Drug Administration (FDA)'s Adverse Event Reporting System have described occurrences of hair loss following initiation of a GLP-1 receptor agonist, particularly semaglutide (Wegovy and Ozempic) and tirzepatide (Mounjaro).
'In response, the FDA has indicated that it is evaluating this potential safety signal.
'Although hair loss does not typically result in physical harm, it may have significant psychosocial consequences, affecting self-esteem, quality of life, and adherence to treatment.'
On the reasons why people may suffer hair loss while on the drugs, the team said the 'most likely mechanism' relates to weight loss and 'reduced caloric intake', though more research is needed.
They said restricting calories may 'contribute to physiological stress and micronutrient deficiencies (for example, iron, zinc, biotin), which can disrupt the hair growth cycle'.
Other factors may include the 'metabolic, hormonal, and immunological effects attributed to GLP-1 receptor agonists that may influence hair follicle growth and cycling'.
For example, GLP-1 receptor agonists have been associated with changes in thyroid function, and delayed gastric emptying may alter the absorption of orally administered drugs, including thyroid hormone or sex hormone therapies, they said.
'Such changes could influence hair growth through endocrine mechanisms, particularly in individuals with underlying hormonal conditions.'
The team concluded: 'Our findings extend previous anecdotal safety signals and provide more systematic evidence to inform clinical awareness of this potential adverse effect.'
GLP-1 drugs, which work by mimicking hormones that regulate appetite, have been shown to tackle a range of chronic diseases and aid substantial weight loss.
The drugs watchdog NICE says around 3.4million obese people in England could benefit from Mounjaro but NHS England has adopted a staggered rollout, with only around 220,000 of the fattest and sickest patients able to access the jabs in the first three years.
More than a quarter (28 per cent) of adults in England are obese and a further 36 per cent are overweight but rationing means most of the estimated 2.5million users in Britain are forced to buy them privately for up to £300 a month.
Responding to the study findings, Dr Marie Spreckley, a weight management researcher at the University of Cambridge, said the absolute risk of suffering hair loss on the drugs remains low at 6.91 cases per 1,000 person-years among GLP-1 users.
She added: 'Overall, this study provides important evidence that clinicians and patients should be aware of this potential adverse effect, but it should be interpreted in the context of the substantial and well-established benefits of GLP-1 receptor agonists for improving glycaemic control, reducing body weight, and lowering the risk of obesity-related complications.
'For many people, those benefits are likely to outweigh this relatively small potential risk.'
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