The National Pharmacy Association (NPA) has urged people not to buy fake weight loss injections - as shortages of Ozempic are expected to continue into next year.
The association warned of a possible "explosion in the unlicensed sale of medication online" and said people were risking their health by purchasing Ozempic and Wegovy (semaglutide) without proper checks.
Ozempic is available on the NHS for people with type two diabetes, while Wegovy can be prescribed for weight loss via specialist weight management services, with strict criteria around who can get the drugs.
But the jabs have exploded in popularity, with social media showing before and after pictures of fat loss, and some celebrities have endorsed their use.
Ozempic, made by Novo Nordisk, helps people with type two diabetes regulate their blood sugar levels but its ability to suppress appetite has also led to people using it to lose weight.
Pharmacists are seeing a shortage of the drug, fuelled by high demand - plus the fact some medics are prescribing it off-label for obese people.
This has led to a shortage for those with diabetes, while also fuelling a rise in counterfeit jabs.
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Risk rising due to 'precarious state of supply'
The NPA, which represents more than 5,000 independently-run community pharmacies, is urging patients to speak to their pharmacist or GP instead of buying medicines online from sellers who are not registered and regulated in the UK.
Nick Kaye, chairman of the NPA, said that pharmacists remain "deeply concerned".
"Stocks of Ozempic are very depleted in community pharmacies in the UK and it is important that these remain prioritised for those in the most clinical need," he said.
"Given the precarious state of supply of this and other vital medication, there is a much greater risk of people looking to order in supplies from disreputable online vendors.
"Wegovy stocks aren't too bad at the moment, it's Ozempic that is problematic."
"We've been told those stocks aren't going to come back in in 0.25(mg), 0.5mg or 1mg doses until 27 December," he added.
"That's the current projected date from the manufacturers themselves.
"In all of our experience, it's much less likely to be earlier than that date and much more likely to be later."
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'We really worry about the fakes'
People often start Ozempic on the lowest dose of 0.25mg before moving up through the levels if needed.
In January, the Department of Health and Social Care told healthcare providers not to prescribe the drugs off-label for weight loss, and said existing stock must be reserved for patients with type 2 diabetes.
It said "supply issues have been caused by an increase in demand for these products for licensed and off-label indications" and supply is "not expected to return to normal until at least the end of 2024".
Mr Kaye added: "We really worry about the fakes within the supply chain.
"People want to access these drugs and when they can't because they're out of stock, they can end up going elsewhere.
"In the UK, we do have regulated and safe online supply in places.
"We're not saying all online [sales] should be banned but we want to make sure it's the right type of organisation and accredited."
Read more:
What are the injections and do they do?
Stephen Fry reveals Ozempic made him vomit
Jabs linked to condition that causes blindness
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Unauthorised sales 'could be dangerous'
Mr Kaye said people can do checks to see if an online provider is registered and regulated by the General Pharmaceutical Council or Pharmaceutical Society of Northern Ireland.
The NPA also wants to see a reintroduction of rules that make it mandatory for a list of regulated online UK medicine sellers to be publicly available.
In June, the World Health Organisation issued a medical product alert over fake semaglutide stocks detected in Brazil, the UK and the US.
It said there have been increasing reports of false semaglutide since 2022.
Meanwhile, the US Food and Drug Administration has warned against people overdosing on the drugs, with reports of some people suffering severe nausea, vomiting, headache, dehydration, pancreatitis and gallstones.
A Department of Health and Social Care spokesman said: "We strongly advise the public not to buy regulated medicines from unauthorised online retailers or beauty salons as they could be dangerous.
"The Medicines and Healthcare products Regulatory Agency continuously works to identify those unlawfully trading in medicines and will use its powers to take appropriate enforcement action, including, where necessary, prosecuting those who put people's health at risk.
"Separately, we are taking action to tackle the obesity crisis head on - shifting our focus from treatment to prevention - which will ease the strain on the NHS and helping people to live well for longer."