People prescribed semaglutide, sold as Ozempic and Wegovy, to lose weight, may have a higher risk of developing a serious but rare eye condition, a study suggests.

Analysing 17,000 patients over six years, US researchers found those taking the drug for type 2 diabetes were four times more likely to be diagnosed with the condition than patients not on the drug.

Among those taking it for obesity, the risk of the condition was seven times higher.

But the researchers cannot prove semaglutide caused the eye condition, which can lead to loss of vision in one eye, nor can they explain the increased risk or the difference between the groups. The numbers affected were small.

Novo Nordisk, the company that makes the drug, said patient safety was “a top priority” but the study had lots of limitations.

Trials show semaglutide can help people with obesity lose more than 10% of their body weight, if they also make changes to diet and lifestyle.

There has been huge hype around the drug after celebrities on social media starting posting about their sudden weight loss while taking it.

Despite it being available on prescription only to people with type 2 diabetes (Ozempic) and the most obese (Wegovy), online pharmacies are selling semaglutide injections with few checks on the weight or underlying health of the person buying them.

And as a result, health bosses say they are worried the drug is being misused as “a quick fix” for people trying to get “beach-body ready”.

All medicines carry potential side-effects.

Some of the most common for semaglutide include:

• nausea
• vomiting
• diarrhoea
• stomach pain
• constipation

A change in vision is listed as one of the more serious potential side-effects, on both Ozempic and Wegovy’s safety information for patients.

Non-arteritic anterior ischemic optic neuropathy (NAION), affects up to 10 out of 100,000 people in the general population, the researchers, from Harvard Medical School, report in journal JAMA Ophthalmology.

It is thought to be caused by reduced blood flow to an optic nerve and cannot currently be treated.

The study revealed:

• 17 cases among type 2 diabetes patients taking semaglutide
• six cases among type 2 diabetes patient taking other drugs
• 20 cases among overweight and obese patients taking semaglutide
• three cases among overweight and obese patients taking a different drug

Harvard Medical School ophthalmology professor Dr Joseph Rizzo said: “Our findings should be viewed as being significant but tentative, as future studies are needed to examine these questions in a much larger and more diverse population.”

UK eye experts from the Royal College of Ophthalmologists recommend patients taking semaglutide are informed of the small risk of developing eye diseases.

Because of the small numbers of patients affected by the eye condition in the study – who may not have been taking their medication as prescribed or be representative of the wider population – the statistics on risk may not be accurate.

Novo Nordisk said the study did not take into account whether patients smoked or for how long they had had diabetes. And there were challenges in accurately coding and identifying cases of the eye condition.

A spokesperson said: “NAION is not listed as a known adverse drug reaction” for marketed formulations of semaglutude – Ozempic, Rybelsus and Wegovy.

“Semaglutide has been studied in large real-world evidence studies and robust clinical development programmes.”

The drug is also being examined in a trial called Focus, which concludes in 2027, to assess its long-term effects on diabetic retinopathy – an eye condition in type 2 diabetes patients.

Queen’s University Belfast honorary professor of physiology Graham McGeown said: “Given the rapid increase in semaglutide use and its possible licensing for a range of problems other than obesity and type 2 diabetes, this issue deserves further study – but possible drug side-effects always need to be balanced against likely benefits.”