A peptide is a short chain of amino acids linked by peptide bonds, typically defined as containing between 2 and 50 amino acids, distinguishing it from a protein, which contains 50 or more. The human body produces thousands of naturally occurring peptides that serve as signalling molecules, hormones, neurotransmitters, and growth factors, regulating virtually every biological process from metabolism and immune function to tissue repair and cognitive performance. Therapeutic peptides are either identical to naturally occurring sequences or modified versions designed to bind the same receptors with enhanced potency, selectivity, or stability.
How Peptides Work
Peptides exert their biological effects primarily by binding to specific receptor proteins on the surface of target cells. This binding triggers intracellular signalling cascades that alter gene expression, protein synthesis, enzyme activity, or cellular metabolism. Because receptors are highly specific for their binding partners, therapeutic peptides can target particular tissues and biological processes with specificity that is difficult to achieve with small-molecule pharmaceuticals. Growth hormone-releasing peptides, for example, bind specifically to ghrelin receptors in the pituitary gland, stimulating growth hormone release without the off-target effects of synthetic growth hormone administration.
Classes of Therapeutic Peptides
Therapeutic peptides used in wellness contexts are typically categorised by their primary biological target. Growth hormone secretagogues stimulate the pituitary to release growth hormone, producing effects on body composition, recovery, and sleep quality. Tissue repair peptides promote healing in specific tissues including tendons, muscles, and the gastrointestinal lining. Antimicrobial peptides support innate immune function. Melanocyte-stimulating peptides affect pigmentation, libido, and energy. Longevity peptides, including the epithalon class, have been studied for their effects on telomerase activation and biological ageing.
Regulatory Status and Safety Considerations
The regulatory status of peptides varies significantly by jurisdiction and intended use. Insulin and glucagon-like peptide-1 analogues such as semaglutide are pharmaceutical-grade peptides licensed as medicines and dispensed through the NHS and private prescribers. Research peptides, sold for laboratory research purposes, occupy a grey regulatory area in the UK, where they are not licensed as medicines but are not classified as controlled substances. Anyone considering therapeutic peptide use should understand the distinction between licensed pharmaceutical peptides prescribed by a registered practitioner and research peptides purchased independently, and the different safety and quality assurance frameworks that apply to each.
Quality and Purity Considerations
Peptide quality varies dramatically between sources. Pharmaceutical-grade peptides undergo rigorous purity testing. Research peptides from specialist suppliers typically include certificate of analysis data from third-party testing, but quality control is not standardised across the industry. Purity above 98 per cent is typically cited for research-grade peptides; below this threshold, impurities may include residual solvents, bacterial endotoxins, or incomplete synthesis products that carry safety concerns. Anyone using peptides should source only from suppliers providing current, third-party verified certificates of analysis.