what do we really know about peptides?

Experts say unregulated peptide sellers could be tiptoeing around regulations by labelling them as "research chemicals" or "not for human consumption".

The increase in imports and sales of unregulated peptides prompted medical regulator, Medsafe, to issue an alert in May. It warned that claims such as "clinically proven", "safe", "approved", or "for research purposes only" did not make these products legal or safe.

SHORE & Whariki Drug Team researchers Chris Wilkins, Marta Rychert and Robin van der Sanden say most unregulated ones have not undergone the clinical safety evaluations required to be sold as legal medicines.

Before and after images of a person using melanotan-II.

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Do you have an experience with peptides? Or are you a medical professional with concerns? Get in touch [email protected].

"This mislabelling and unethical marketing allows the trade to flourish in a legal grey zone between approved and unapproved medicines, potentially putting people at risk of health issues."

Hype is building around peptides with health and wellness influencers promoting them for their purported benefits. The latest Therapeutic Goods Administration data out of Australia showed it requested 3263 "wellness and beauty industries unapproved high risk therapeutic goods advertising" online and social media advertisements to be removed, which captures unlawful peptide advertising.

Unregulated peptides seized by Medsafe.

Supplied / Medsafe

What are peptides?

Pharmacist Rhys Ponton, a senior lecturer at the University of Auckland (UoA), says peptides are chains of amino acids - the building blocks of proteins - synthesised to trigger specific biological responses in the body.

"The desired effects of use range from enhancing performance or changing the appearance of the body through weight loss, muscle gain or other effects, such as producing a sun-tanned look."

Professor Clare Wall, head of UoA's School of Medical Sciences, says our bodies also naturally produce peptides. They generally stimulate the body to release hormones or activate specific cellular pathways. For example, they can be involved in blood sugar control, appetite regulation and immune function.

Professor Clare Wall, head of University of Auckland's School of Medical Sciences

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UoA professor of cell signalling Peter Shepherd says peptide hormones control all sorts of processes in our bodies "and drug companies not only produce all sorts of natural peptide hormones (e.g. insulin) but have also figured out how to modify the natural peptide hormones to make them even more effective".

"Wegovy is an example of that. One problem though with peptides is that they are rapidly broken down in our stomach, so most peptides have to be injected."

The SHORE & Whariki Drug Research Team notes some peptides can be taken orally or applied topically but agree the most effective and common form of administration is via self-administered injection.

Are the claims behind them backed up?

Some purported claims about peptides include anti-ageing, tanning, injury recovery, muscle building, weight loss and cosmetic skin benefits.

However, Wall says there are very few robust long-term clinical trials proving IV peptides are effective and safe.

"Much of the evidence is from laboratory studies or animal studies, anecdotal reports and very small human studies.

"However, for some of the medical grade peptides such as Semaglutide and liraglutide there is substantial evidence showing benefits of weight loss etc."

DISC Trust national harm reduction lead Jason George adds that claimed benefits often exceed what has been demonstrated in studies.

Jason George, the national harm reduction lead for DISC Trust.

Rachel Graham / RNZ

"Many people report benefits from using peptides, but personal experiences and anecdotal reports are not the same as scientific evidence.

"For many products, much of the evidence comes from laboratory or animal studies which don't always apply to humans."

What are the risks?

Medsafe has warned products that are not prescribed by a doctor or sourced from a pharmacy "are illegal and potentially harmful. Using them can cause serious and potentially life threatening reactions".

The SHORE & Whariki Drug Research Team also strongly advises against injecting unregulated chemicals, saying it can lead to injuries, infections, or the transmission of serious diseases such as Hepatitis C if needles are reused or shared.

"Additionally, the lack of regulation and mislabelling of products means that there is potential for peptides to be contaminated or to contain an entirely different substance than advertised."

Wall agrees, saying independent testing has found incorrect doses, contamination and different compounds. There are also concerns about abscesses, damage to tissue or blood vessels, as well as uncertainty over long-term effects on hormonal pathways, including water retention, joint pain, increased blood sugar and insulin resistance.

Ponton says peptides are commonly sold as freeze-dried powder that requires reconstitution before injection. Over- or under-dilution can result in a product that is stronger or weaker than intended.

"Peptides are fragile molecules and require careful storage to reduce degradation.

"As products sourced from a market without careful temperature regulation (a 'cold chain'), they may have degraded by the time they have been received. Once diluted, they will degrade more rapidly and careful storage is vital."

Shepherd warns it is easy to get the dose wrong - and the consequences can be severe because peptides target hormonal systems.

Large moles similar to these appeared on the young person's back after they used melanotan-II.

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While there is no published research on unregulated peptide use in New Zealand, the 2026 New Zealand Drug Trends Survey aims to collect local data on patterns of performance-enhancing drug and peptide use, and associated harms.

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