Alarm over ‘substitutes’ sold on black market as Mounjaro price bloats

From tomorrow, American pharma giant Eli Lilly will raise the price of its Mounjaro drug by up to 170%, prompting pharmacies and health professionals to warn of cheaper counterfeit medication being marketed online and on social media.

Andy Morling, head of the criminal enforcement unit of the Medicines and Healthcare products Regulatory Agency (MHRA), said that “sourcing any medicine from unregulated suppliers significantly increases the risk of getting a product which is either falsified or not approved for use”.

He added: “Products purchased in this way… can expose patients to incorrect dosages, or dangerous ingredients that can have serious health consequences.”

More than 18,300 illegal weight-loss products, including fake Mounjaro pens, were seized by the UK Border Force between January 2024 and June 2025, according to a recent freedom of information request by the online pharmacy, Chemist4U.

Jason Murphy, head of pharmacy at Chemist4U, told The Observer that the “true scope of counterfeit Mounjaro pens is likely not yet fully realised”, adding: “As the market is squeezed by more limited stocks, we can expect more illicit pens to be produced to fill the gap and put even more patients at real risk.”

Eli Lilly said that patient safety was its “highest priority”. A spokesperson said: “People who purchase counterfeit or black market medicines (those sold from unregulated sources) have no way of knowing what they actually contain… No one should ever risk putting them into their bodies.”

Dr Luke Turnock, a criminology lecturer at the University of Lincoln who studies the online black market for weight-loss drugs, told The Observer that as well as counterfeit Mounjaro, he has seen an increase in sellers offering retatrutide illegally in the UK.

Retatrutide is a drug produced by Eli Lilly that is still in clinical trials; it has not received clinical approval from the MHRA and it is illegal to sell it for personal use.

Turnock told The Observer that over the past year he has seen a sharp rise in users illegally claiming to sell retatrutide in the UK, often by the same dealers who illegally supply steroids to the fitness and bodybuilding community.

His research suggests dealers are sourcing retatrutide in bulk from China for as little as £1.50 per vial, then reselling it in the UK at a substantial markup.

A spokesperson for Eli Lilly warned that retatrutide “has not been reviewed or approved by any regulatory agency anywhere in the world, and therefore at this time no one can sell retatrutide for human use”.

The spokesperson added: “Any product falsely representing itself as a Lilly investigational product not yet approved by any regulatory agency, like retatrutide, may expose patients to potentially serious health risks.”

The MHRA told The Observer that it was aware of reports of products being sold online and through social media platforms, including TikTok, that claim to contain retatrutide.

“Outside of authorised clinical trials, any products being sold in the UK that claim to contain retatrutide are likely to be illegal and potentially dangerous,” the regulator said.

The Observer has found posts on TikTok, Reddit and Facebook from people in the UK who take Mounjaro asking for advice on how to secure retatrutide from unregulated online buyers in response to the increased cost.

A spokesperson for TikTok said it had banned searches for retatrutide, or “reta”, on its platform and said its community guidelines make it clear that “we don’t allow trading, marketing, or providing access to regulated, prohibited, or high-risk goods and services”.

Last week, a video from a TikTok user mentioning retatrutide had more than 490,000 views suggesting users “switch” from Mounjaro.

The user’s profile linked to an online shop offering retatrutide for about £120, and claiming that its products are “manufactured and distributed in line with current UK guidelines”. The video was later taken down.

Duncan Rudkin, the chief executive of the General Pharmaceutical Council, warned that “anyone using illegal websites is taking a huge risk with their health, as they may receive counterfeit medicines that contain dangerous ingredients”.

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