A growing trend of self-injecting unapproved peptides for fitness and wellness purposes is raising serious health concerns, with experts warning that many of these substances have not been properly tested in humans.
Peptides, which are short chains of amino acids, play key roles in the body and are used in some approved medicines. However, specialists say a rising number of online sellers and social media influencers are promoting experimental compounds as quick solutions for muscle growth, weight loss, better sleep, improved skin and anti-aging.
Many of these claims are not supported by large human studies. Instead, they often rely on laboratory research, animal testing or personal testimonials, according to health experts.
The trend has led some users to buy injectable peptides online and use them without medical supervision. In France, one user reported injecting compounds such as GHK-Cu, believed to improve skin, and retatrutide, an experimental drug being studied for weight loss. Neither is approved for routine self-treatment.
Scientists warn that knowledge about the safe use of many of these substances remains limited. France’s National Institute of Health and Medical Research (Inserm) has said there is no strong clinical evidence confirming many of the benefits widely promoted online. It also warned that some products pose “very real” health risks.
Concerns are not only theoretical. In June, Australian authorities reported six cases of acute liver injury linked to products labeled as retatrutide. While it is unclear whether all the products contained the same ingredients, experts say the cases highlight the dangers of poorly regulated or misidentified substances.
Health professionals caution that peptides bought online may not contain what their labels claim, may have incorrect doses or could be contaminated during production.
Another trend involves the use of melanotan, sometimes called the “Barbie peptide,” which is promoted online as a way to achieve a darker skin tone. The substance is not approved for tanning, and doctors have warned of side effects including facial flushing and changes in moles. They also say it may encourage increased sun exposure, raising the risk of skin cancer.
Experts advise consumers not to assume that products marketed as “research peptides” are safe. The term often indicates that the substances are intended for laboratory use, not for human treatment.
They recommend that anyone considering peptide-based treatments should check whether the product is approved by national regulators and consult a qualified medical professional.
While approved peptide medicines have important uses, specialists warn that the rapid growth of the online peptide market is outpacing scientific evidence, increasing the risk for users seeking quick health and appearance gains.