Weight-loss drugs are everywhere. You only need to scroll on social media, open the papers, or see the rise of ‘ozempic menus’ in restaurants (yep, that’s a thing) to realise just how prevalent drugs such as Wegovy and Mounjaro have become.

The figures back this up. Polling in 2024 found that one in five Britons would use a weight-loss drug if it was free on the NHS, according to polling that also shows one in seven have either taken a jab themselves or know someone who has.

Lots has been reported on the negative side-effects of weight-loss drugs, from stomach problems to changes in vision and bad breath (known as Ozempic teeth). But new research points to a surprising new side-effect of the drugs, which isn’t necessarily as bad as some of the others.

A new study by the St Louis University Hospital in Missouri, USA, has found that injections such as Wegovy and Mounjaro can boost men’s testosterone levels. The research built on previous studies that show weight loss surgery or lifestyle changes can increase testosterone levels in the body. The researchers tracked 110 men in their 40s, 50s and 60s, who were on semaglutide, the active ingredient in weight loss jabs that stops users feeling hungry. The mean age of the participants was 54.

At the beginning of their treatment just 53 per cent of the men had normal testosterone levels. What’s considered ‘normal’ for testosterone levels can fluctuate greatly, although average levels typically range from 300 to 1000 nanograms per deciliter (ng/dL). When testosterone levels are low, it can cause a range of symptoms, including fatigue, weakness and fat gain, depression, brain fog, and a lack of desire or inability to perform in the bedroom. Testosterone tends to decline gradually with age, starting around the late 30s to early 40s. Boosting testosterone to normal levels for people with low testosterone can improve low sex drive, but it’s worth noting that increasing testosterone levels above that will not help.

The surprise new research found that after eighteen months of treatment with weight-loss jabs, the number of men with healthy testosterone levels increased to 77 per cent.

So, what’s likely going on here? Lowered testosterone levels are not unusual in men with obesity or type 2 diabetes. This is usually rectified through weight loss and improved insulin regulation. Because weight-loss drugs help users shift extra pounds and control blood sugar levels, it makes sense that improved testosterone levels follow suit.

Of course, research around this topic is still in very early stages. It’s worth noting that the findings don’t prove the increase in testosterone levels was caused by the drugs semaglutide or tirzepatide. Researchers are hoping that more in-depth studies will confirm the connection.

The increases we observed were more modest than what you would typically see with testosterone replacement therapy,’ said lead author of the study Dr. Shellsea Portillo Canales, endocrinologist at SSM Health St. Louis University Hospital, via email. ‘However, they occurred naturally, without testosterone replacement therapy (TRT), and likely reflect the body recovering its normal hormone production as weight and insulin resistance improved.’

She added that the research highlighted the need to for men already on testosterone therapies to track their levels after starting weight loss medications.

This isn’t the first time that weight-loss drugs have been linked to sexual function. Some reports suggesting that they actually have the opposite effect. A study published in May 2024 found that men with obesity who were taking semaglutide actually at a slightly higher risk of erectile dysfunction than men with obesity who weren’t taking the drug. Meanwhile on Reddit, many men have taken to the forum to express their concern about erectile dysfunction and Ozempic. Users reported everything from ‘less drive’ to a libido ‘through the roof.’

Another recent study published in the International Journal of Impotence Research found that men between the ages of 18 to 50 who took semaglutide for weight loss, but not diabetes, were more likely to develop erectile dysfunction and low testosterone levels than men who didn’t use the meds.

‘We know that weight loss generally has a positive effect on testosterone levels and sexual function, and as it turned out, the data showed the exact opposite,’ says study author Joseph Sonstein, MD, assistant professor of surgery in the Division of Urology at the University of Texas Medical Branch.

There are other surprising side-effects that have been linked to weight-loss jabs. Research indicates that people taking Wegovy are likely to have a lower risk of heart attacks and strokes, so the drug not only helps with weight loss but your heart health too. Weight loss drugs have also been linked to reducing the risk of kidney disease and treating sleep apnea.

However, like with any new research related to Ozempic, it’s important to stress that this is still in the early stages. It’s still possible that semaglutide is affecting our bodies in ways we are still in the process of discovering – sex and all.