A peptide is a short chain of amino acids connected by peptide bonds. Two amino acids make a dipeptide; three make a tripeptide; somewhere in the range of 50 to 100 amino acids the term "peptide" gives way to "protein", though the boundary is not sharp. The peptides discussed on this site range from three amino acids (Pinealon) to fifteen (FGL), with most sitting in the six-to-nine range typical of the bioactive-fragment tradition.

Bioactive peptides occur naturally throughout the body. Hormones (insulin, oxytocin), neurotransmitter modulators (substance P, the enkephalins), growth factors (BDNF, NGF), and immune mediators (tuftsin, defensins) all include peptides among their members. Synthetic research peptides are usually engineered either as extensions or modifications of these natural sequences, or as mimetics of specific binding motifs in larger proteins.

The molecular logic of "design a short peptide that copies the active part of a long protein" is what produced FGL (mimicking the NCAM-FGFR1 binding motif), Dihexa (mimicking the active fragment of angiotensin IV), and Selank (extending the endogenous tuftsin sequence for stability). Once you grasp this design pattern, the field becomes less mysterious.

The term "research peptide" is not defined in the UK legislation cited on this site. Which rules apply depends on whether a substance is a controlled drug (Schedule 2 to the Misuse of Drugs Act 1971), a medicinal product (regulation 2(1) of the Human Medicines Regulations 2012) or a psychoactive substance (section 2 of the Psychoactive Substances Act 2016). The same chemistry can be a registered medicine in one country (Semax in Russia, per Vidal.ru) while no entry for it was found in the UK electronic medicines compendium on 17 October 2026.

The practical implication is that research-grade peptides do not come with the product information (summary of product characteristics, patient leaflet) that accompanies an authorised medicine. Purity and batch consistency should be checked, and evaluating a supplier (HPLC certificates, mass spectrometry confirmation, batch documentation) matters at least as much as evaluating the underlying compound.

Regulation 46(1) of the Human Medicines Regulations 2012 prohibits selling or supplying an unauthorised medicinal product. Supplier material that provides dosing instructions, before-and-after photographs, or other framing that suggests human use is a red flag about both their regulatory position and the seriousness of their operation.

The delivery problem is central to the peptide research literature. Peptides cannot be taken orally as a default: they are degraded by gastrointestinal proteases before they reach systemic circulation. Three workarounds dominate the research-peptide field.

Intranasal administration is the standard route for the Russian-origin cognitive peptides (Semax, Selank, and their acetylated analogues). The nasal mucosa supports direct nose-to-brain transport via the olfactory and trigeminal pathways, bypassing the bloodstream and the blood-brain barrier. The bioavailability is sub-parenteral but the route is reproducible and clinically practical.

Parenteral administration (subcutaneous, intramuscular, intravenous) is used where the peptide is large or unstable enough that intranasal delivery is insufficient. Cerebrolysin's standard administration in approving jurisdictions is by intravenous infusion; many synaptogenesis research peptides are studied by subcutaneous injection in animals.

Oral administration is the exception, not the rule. It works for specifically engineered peptidomimetics — Noopept's ester chemistry survives the gut; Dihexa's particular structure achieves measurable oral bioavailability in animal research — but it is not available for most of the peptides on this site.