Peptides are one of the fastest-moving areas of health and medical research — and one of the most misunderstood. This guide covers what they are, how they work, every major category being researched today, and how the evidence stacks up.
This is an educational resource only. Nothing here constitutes medical advice. Always consult a qualified healthcare practitioner before considering any peptide therapy.
Short signalling molecules with an outsized role in modern medicine — small enough to slip into cells, specific enough to act on a single pathway.
Peptides are short chains of amino acids — the same building blocks that make up proteins. The difference is size: proteins typically contain hundreds or thousands of amino acids folded into complex structures, while peptides are usually between 2 and 50 amino acids long. That smaller size is what gives many peptides their power as signalling molecules — they're compact enough to pass through cell membranes, bind to specific receptors, and trigger precise biological responses.
Your body already produces hundreds of peptides naturally. Insulin is a peptide. So is oxytocin, glucagon, and most growth factors.
Many of the peptides researched for health applications are either identical to, or closely modelled on, these naturally occurring compounds — which is part of why researchers find them interesting in the first place.
What makes peptides particularly exciting to researchers is their specificity. Unlike many drugs that affect multiple systems broadly, peptides often interact with a single receptor type or signalling pathway — making them, in theory, capable of more targeted effects with fewer off-target consequences. In practice, the picture is more complicated, but that specificity is the founding principle of most peptide drug development.
Brand names: Wegovy (weight management), Ozempic (diabetes)
A GLP-1 receptor agonist approved by the MHRA for chronic weight management and type 2 diabetes. Available on NHS prescription for eligible patients in England, Wales, and Scotland, subject to clinical criteria and ongoing supply.
Phase III STEP trial data demonstrated average weight reductions of 14.9% over 68 weeks at 2.4mg weekly.
Brand names: Saxenda (obesity), Victoza (diabetes)
A daily GLP-1 agonist and predecessor to semaglutide, with MHRA approval for both obesity and type 2 diabetes. Requires daily rather than weekly injection.
SCALE trial data showed average weight loss of 8.4% over 56 weeks.
Brand names: Mounjaro (diabetes), Zepbound (weight management)
A dual GIP and GLP-1 receptor agonist — the first medicine to activate both receptors simultaneously. MHRA-approved for type 2 diabetes, with a weight management indication also granted.
SURMOUNT-1 trial data showed average weight reductions of up to 22.5% — surpassing every previously approved medicine in its class.
Developer: Eli Lilly — Phase III trials ongoing
The most closely watched peptide in current obesity medicine. Where semaglutide activates one receptor and tirzepatide activates two, retatrutide is a triple agonist — targeting GLP-1, GIP, and glucagon receptors simultaneously. It has no MHRA authorisation as of 2025 and is not available outside clinical trials. It represents where the science is actively heading.
Phase II results showed average weight reductions of up to 24.2% over 48 weeks — the highest figure ever recorded for any pharmacological weight loss intervention in clinical trials.
The most clinically mature category, anchored by the GLP-1 class. Extends to growth hormone secretagogues for fat oxidation, AOD-9604 as a targeted lipolytic, and emerging triple agonists like Retatrutide currently in Phase III trials.
Peptides for musculoskeletal healing, muscle growth, and recovery. Includes tissue repair compounds, anabolic growth factors, and GH secretagogues.
Note: Several are on the WADA Prohibited List and enforced in the UK by UKAD.
Research at the frontier of ageing biology, targeting telomere attrition, mitochondrial dysfunction, cellular senescence, and immunosenescence.
Primarily developed in Russian research. Targets neuroprotection, BDNF pathways, and cognitive enhancement.
The most publicly accessible category, with popular compounds widely used in topical formulations.
Note: These fall under UK Cosmetics Regulation rather than medicines law.
Five categories, five very different evidence bases. The next section explains how to weigh any peptide claim against the strength of the research behind it.
Clear, evidence-graded answers to the things people ask most about peptides — without the hype or the small print.
Explore the Guide