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People in the UK are sending thousands of unregulated substances that claim to support weight-loss and wellness to laboratories for testing, as experts say the underground market for injectable peptides has exploded.

The peptide-testing industry has expanded rapidly alongside demand for these substances, with one lab telling the Guardian that a decade ago, they handled a handful of tests a month sent by customers and vendors around the world to check what was in them. Today, they process around 60,000 samples a year, including roughly 2,000 orders from the UK since 2024.

Peptides are short chains of amino acids. These can be found naturally in the body – for example hormones, such as insulin, oxytocin and vasopressin are peptides – but they can also be made synthetically in the laboratory.

They include the active ingredients in prescription weight-loss drugs, such as Wegovy, which mimic the natural hormone GLP-1, as well as in experimental compounds pushed online by the booming biohacking and anti-ageing industries. On Telegram and TikTok, users claim the injections can heal injuries, sharpen focus and smooth wrinkles.

Unlike medicines such as Wegovy, however, many of these experimental peptides are unapproved by regulators, with experts warning the compounds lack reliable safety data and quality control. Many are sold with labels stating they are “for research purposes only”, even as customers inject them into their bodies.

Finnrick, a peptide testing laboratory in Texas, said about a third of the thousands of products it analysed failed basic quality checks, and that proportion had stayed broadly unchanged over the 12 to 14 months it had been gathering data.

The failures typically fall into three categories: identity, meaning the substance is not what the label claims; purity, with anything below the 98% threshold considered substandard; and quantity, where the vial contains either more or less than the stated milligram dose. The result, the lab said, was that buyers were frequently not receiving the compound, or the amount, for which they believed they had paid.

Finnrick typically buys peptide products itself for testing, saying it prefers to analyse samples bought through the same channels used by ordinary customers rather than accepting products directly from vendors. In June last year, the lab also began accepting samples submitted by members of the public. Any products that came directly from vendors were flagged as such on its website.

Sometimes these peptides are essentially bootleg versions of approved drugs – such as semaglutide, the active ingredient in Wegovy, or tirzepatide, the active ingredient in the weight-loss jab Mounjaro – but are procured for a fraction of their market price from dealers online.

Because they are sold as compounds “for research purposes only”, and in some cases are not formally classified as medicines, vendors are able to exploit a legal grey area with little regulatory oversight.

Dr Luke Turnock, a senior lecturer in criminology at the University of Lincoln, said: “There are risks that you don’t necessarily know that what you think you’re buying is in fact the product that it claims [to be], and also you don’t know if it’s overdosed or underdosed.

“And in terms of if you do get the correct thing, the main risks are we do not have that long-term clinical data,” he said. “We don’t know the potential harms you could be doing longer term, such as increased cancer risk [or] damage to organs that you might not even perceive whilst you’re using them.”

Peter Magic, a chemist at Janoshik Analytical, a laboratory in the Czech Republic known for testing peptides and performance-enhancing drugs, said the volume of samples arriving for analysis each month had rocketed to 5,000.

“Roughly three or four years ago there was an exponential growth in demand, mostly for peptides,” Magic said, attributing the boom to the arrival of highly effective GLP-1 drugs. “Especially with the advent of semaglutide … we’ve seen an insane explosion with that, then with tirzepatide, and now with retatrutide, which is the most modern one available.” Retatrutide is a weight-loss medication that is being tested in clinical trials and has not yet been approved for use in the UK – meaning it is illegal for the peptide to be sold and supplied.

Magic said the UK was in the vanguard of this explosion in testing. While the US and China dominated the market, he noted that the UK tied with Canada for third place, generating roughly 2,000 testing orders since 2024. “I would say the UK is a rather big peptide market,” he said. “It’s a populous country, and the peptide market is closely related to performance-enhancing drugs. Often it’s the same factories, the same vendors and the same distribution channels.”

The large profit margins were also drawing dangerous players into the supply chain. “You can buy a vial for about $15 from China and sell it on for 10 times that,” Magic said. “That attracts a lot of people, including some nefarious actors. It is easy money, and it is not treated as seriously as selling narcotics or anabolic steroids.”

Analysis of more than 5,000 peptide-related videos on TikTok found that 64% were from US-based accounts. UK creators were the second largest group, making up 16% of the videos.

Prof Amira Guirguis, the chief scientist at the Royal Pharmaceutical Society, said: “Websites that sell peptides in a retail-style way, often with labels like ‘research use only’, sit outside the usual controlled systems. Where substances have biological effects or, when introduced in the body, can change one or more physiological functions, questions about oversight, traceability and quality assurance are vital.”