A patient who tore their oesophagus after taking a counterfeit version of an experimental weight loss drug has prompted Australia’s medicines regulator to warn of serious risks of such products.

The concern relates to retatrutide, a type of drug known as a peptide. Retatrutide has not been approved by the Therapeutic Goods Administration (TGA) or regulators overseas, and it cannot be legally prescribed or sold in Australia.

Related: ‘Who knows what they’re taking?’: people risk the gray market for the newest weight-loss drug

Peptides are strings of molecules called amino acids that act as chemical messengers in the body, and are involved in a range of functions like hormone activity, digestion, immune defence, and tissue growth. The peptides in retatrutide mimic hunger hormones.

Despite being unapproved, the drug has been widely promoted on social media and promoted for sale on the hidden market, with names including retatrutide, Reta, R-10 and R-20, and they often come in unmarked vials.

Sign up for the Breaking News Australia email

The TGA was alerted after someone experienced such severe and uncontrollable vomiting – after taking what they believed was retatrutide – that they tore their oesophagus, which can be life-threatening. They required treatment in hospital.

The TGA obtained a sample of the product and found it contained a different peptide that also targets hunger, called semaglutide, and no retatrutide.

The amount of semaglutide detected was approximately eight times higher than levels found in approved semaglutide products assessed by the TGA.

The TGA’s chief medical adviser, Prof Robyn Langham, said products being sold online may be fake or counterfeit and could contain ingredients that pose serious risks to health.

“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 particularly concerning for injectable products, where contaminated or non-sterile manufacturing can increase the risk of infection and harmful immune responses including anaphylaxis.”

People who self-inject face additional risks such as incorrect dosing, unsafe injection technique and serious adverse reactions, Langham said.

The Victorian health department issued a similar warning in June, after it was notified of six cases of acute liver toxicity associated with products labelled as retatrutide.

The head of the TGA, Prof Anthony Lawler, said imported and illegal products are “not subject to the same controls over the quality or efficacy of the goods when compared with medicines approved for supply in Australia”.

Australia’s chief medical officer has previously issued a public health warning about unapproved and non-prescribed peptides, after reports of serious adverse effects including liver damage, inflammation and severe allergic reactions.