A patient in Australia suffered a severe injury to their oesophagus after taking what they believed to be an experimental weight loss drug called retatrutide. This incident has led Australia’s medicines regulator, the Therapeutic Goods Administration (TGA), to issue a warning about the serious health risks associated with counterfeit or unapproved versions of such drugs. Retatrutide is a type of medication known as a peptide, which is a chain of molecules called amino acids. These molecules act as chemical messengers in the body, playing a role in processes such as hormone regulation, digestion, immune responses, and tissue growth. Retatrutide, which mimics hunger hormones, has not been approved by the TGA or other international regulators and cannot be legally sold or prescribed in Australia. Despite the lack of approval, retatrutide and similar products have been widely promoted on social media and sold on the hidden, or dark, web. These products are often sold under different names, such as Reta, R-10, or R-20, and come in unmarked vials. The TGA became aware of the risks after a person suffered from severe and uncontrollable vomiting, which led to a tear in their oesophagus — a potentially life-threatening condition. Hospital treatment was required. When the TGA examined a sample of the product, they found that it contained a different peptide, called semaglutide, which also targets hunger hormones. The amount of semaglutide detected was about eight times higher than what is found in approved versions of the drug. TGA’s chief medical adviser, Prof Robyn Langham, warned that counterfeit or unapproved peptide products can contain unknown substances, incorrect dosages, or harmful contaminants. “The biggest risks with unapproved peptide products are not knowing what is in the vial, how much of or even what substance it contains, whether it is sterile, or whether it contains other contaminants or toxins,” she said. These risks are especially high for injectable drugs, where poor manufacturing practices can lead to infections or severe allergic reactions, such as anaphylaxis. People who self-inject these drugs also face additional dangers, including incorrect dosing and unsafe injection techniques, which can result in serious adverse effects. In June, the Victorian health department issued a similar warning after six cases of acute liver toxicity were linked to products labeled as retatrutide. TGA head Prof Anthony Lawler emphasized that imported and illegal products are not subject to the same quality and safety controls as medicines approved in Australia. Australia’s chief medical officer has previously issued public health warnings about unapproved peptides, citing reports of serious side effects, including liver damage, inflammation, and severe allergic reactions. These incidents highlight the dangers of using unregulated and unapproved drugs, particularly those obtained through unofficial or hidden markets.