Several compounds sold as peptides are not peptides. The distinction is not pedantry: it changes how a substance behaves in the body and how it is regulated.
Three structural classes
| Class | Size | Typical route | Examples here |
|---|---|---|---|
| Small molecule | Tiny, often under 500 g/mol | Usually oral | 5-Amino-1MQ, NAD+ |
| Peptide | Roughly 2–50 amino acids | Usually injected | BPC-157, semaglutide, oxytocin |
| Protein / glycoprotein | 50+ amino acids, folded | Injected | HCG, IGF-1 LR3 |
Why peptides are usually injected
Digestive enzymes break peptide bonds; that is their function. A peptide swallowed in its native form is largely dismantled before absorption. Oral semaglutide exists only because it is formulated with an absorption enhancer, and even then the dosing differs entirely from the injection.
When a product claims oral or nasal delivery of a peptide normally given by injection, the question worth asking is whether absorption by that route has actually been demonstrated for that molecule.
Half-life explains dosing frequency
Natural GLP-1 lasts minutes. Semaglutide lasts about a week, which is the entire reason it is a weekly injection rather than an impractical one. Oxytocin’s very short half-life is why it is given as a continuously adjusted infusion rather than a fixed dose.
Where regulation differs
- Glutathione and NAD+ precursors are sold as dietary supplements, a category with far lighter requirements than drugs.
- GHK-Cu and AHK-Cu are established cosmetic ingredients. Cosmetic status covers topical use and implies nothing about injection.
- 5-Amino-1MQ is a small molecule sold alongside peptides, with no approval in any category.
Reading a product’s regulatory category correctly prevents a common error: treating "legal to sell" as "reviewed for this use".