How do peptides work?

1. Some peptides are signals

Cells talk to each other with chemical messengers, and some of those messengers are short chains of amino acids. The usual picture is a lock and key: the peptide fits a receptor on or in a target cell, and that starts a change in the cell. This is general biology rather than a finding of any one study on this site, but it is why researchers pay attention to peptides, and it is how the approved peptide drugs, insulin and the GLP-1 medicines among them, are designed to act.

The same idea underlies claims about consumer peptides, with a big difference in how well it is tested. Two examples from the studies here:

• GHK, a three-amino-acid peptide. A review describes it as a natural modulator of many pathways in skin repair, mainly from animal and cell work, and reports it can raise or lower the activity of thousands of genes (Pickart 2015). Changing gene activity in a dish is a mechanism hint, not a clinical result.
• Valyl-tyrosine, a two-amino-acid peptide from sardine. This is the rare case where the proposed mechanism was checked in people. In a small randomised trial, blood pressure fell on the peptide and not on placebo, and blood markers fitted blockade of ACE, an enzyme that helps tighten blood vessels (Kawasaki 2000). It was 29 people over four weeks, and nothing else here replicates it.

2. Swallowed peptides meet digestion

Food protein is broken into smaller pieces and amino acids by digestion, and a peptide in a powder or capsule enters the same system. So for oral products there are two separate questions: does anything active get through, and does it do anything if it does. Neither is settled by the label.

A small crossover study shows how easily the first question gets blurred. After exercise, fish protein hydrolysate raised blood amino acids about as much as whey hydrolysate did, which shows it is digested quickly. It says nothing about effects from specific bioactive peptides (Cordeiro 2020; nine people). For what the oral trials found on outcomes, see Do oral marine peptides work? and the evidence for skin.

3. Injecting skips digestion, not risk

Injected peptides avoid the gut, which is one reason people use them. They also bring injection risks and depend on how the product was made. A 2026 review of approved and unapproved peptides found that many unapproved ones look favourable in animals, while rigorous human safety data are scarce and serious harm is possible. Reviews of BPC-157 describe a compound with a lot of animal work behind it and very little in people (Vasireddi 2025: 35 preclinical studies and one clinical report).

4. A mechanism is not the proof

“It blocks an enzyme” or “it switches on repair genes” sounds like an explanation. It is a reason to run a trial. Many things that work in cells or animals do nothing in people, and the people who sell a product can quote a mechanism without ever testing it in humans. A 2026 scoping review found that 67% of the publications it searched on six popular injectable peptides used animal models, and concluded the claimed benefits remain unsubstantiated by human trials.

When you read a claim about how a peptide works, ask: was this shown in people, in animals, or in cells? Did the study measure a real outcome, or only a marker? Was there a comparison group? We answer those questions for each study on the studies hub, and explain how in the methodology.