The four ways peptides are taken
Nearly every peptide reaches the body through one of four routes. Which one depends on whether the peptide can survive digestion and where it needs to act:
| Route | How it's given | Why it's used | Examples |
|---|---|---|---|
| Injection | Usually subcutaneous (under the skin); sometimes intramuscular | Bypasses digestion entirely — the default for most peptides | Semaglutide, tirzepatide |
| Oral | Tablet, with a special formulation or a gut-local target | Only works for peptides protected from stomach acid, or ones meant to act in the gut | Rybelsus, linaclotide |
| Nasal | Intranasal spray | Avoids the gut; can offer more direct access toward the brain | Semax, Selank |
| Topical | Cream or serum applied to the skin | For cosmetic peptides designed to act locally in the skin | GHK-Cu, Argireline |
The rest of this guide explains each route — starting with why injection is the default.
Why most peptides are injected
The gut is built to digest proteins and peptides into their component amino acids. An oral peptide therefore faces low oral bioavailability: stomach acid and digestive enzymes degrade it, and little or none reaches the bloodstream intact. Injecting a peptide bypasses digestion entirely, which is why the great majority of therapeutic and research peptides are given as injections — most commonly subcutaneous (into the fat layer just under the skin).
Oral peptides and the bioavailability problem
The reason you can't simply swallow most peptides comes down to bioavailability — the fraction of a dose that actually reaches the bloodstream intact. For most oral peptides this figure is close to zero: stomach acid and protein-digesting enzymes break the chain apart, and the large, water-loving peptide molecule struggles to cross the gut wall even if it survives. That's why an injected peptide can be effective at a tiny dose while the same peptide in a pill may do almost nothing.
A few peptides overcome this through clever workarounds:
- Special formulations. Oral semaglutide (Rybelsus) is paired with an absorption enhancer (SNAC) that briefly shields it from stomach acid and helps a small, consistent fraction cross into the blood.
- Gut-local action. Peptides like linaclotide and plecanatide are meant to act on receptors in the gut itself, so they don't need to be absorbed into the bloodstream at all.
Getting more peptides to work orally is an active area of drug-delivery research, but for now oral options remain the exception rather than the rule.
Nasal sprays
The nasal lining offers another route that avoids the digestive tract. Several neuropeptides studied for the brain — such as Semax and Selank — are formulated as intranasal solutions, partly because this can offer more direct access toward the central nervous system.
Topical (skin) peptides
Cosmetic peptides are applied to the skin as ingredients in serums and creams. Copper peptide GHK-Cu, Matrixyl, and Argireline are designed to act locally in the skin rather than be absorbed systemically, and are regulated as cosmetics.
Frequently asked questions
How are peptides taken?
Peptides are taken by one of four routes: injection (usually subcutaneous, the most common), oral tablets (only for specially formulated or gut-targeted peptides), nasal sprays (mainly neuropeptides), and topical creams (cosmetic skin peptides). The route depends on whether the peptide can survive digestion and where it needs to act.
Why can't most peptides be taken orally?
Peptides are short amino-acid chains, and the digestive system breaks them down before they can be absorbed. This gives most oral peptides very low bioavailability, which is why the majority are injected (usually subcutaneously) to bypass digestion.
Why do peptides have low oral bioavailability?
Stomach acid and digestive enzymes degrade the peptide chain, and the large, water-loving molecule struggles to cross the gut wall even if it survives. As a result, very little of an oral dose reaches the bloodstream intact — often close to zero without special formulation.
Are there any oral peptides?
Yes, a few. Oral semaglutide (Rybelsus) uses an absorption enhancer (SNAC) to survive the stomach, and gut-targeted peptides like linaclotide and plecanatide are designed to act in the intestine itself, so they don't need to enter the bloodstream.
Why are some peptides given as nasal sprays?
The nasal route avoids the digestive tract and can offer more direct access toward the brain, which is why several neuropeptides such as Semax and Selank are formulated as intranasal solutions.
How do peptide skincare products work?
Cosmetic peptides like GHK-Cu, Matrixyl, and Argireline are applied topically and are designed to act locally within the skin rather than be absorbed into the body. They are regulated as cosmetics.
Further reading
Selected peer-reviewed sources on this topic, labelled by type. A citation is a reference, not an endorsement.
- Zhang X, Han Y, Huang W, et al. The influence of the gut microbiota on the bioavailability of oral drugs. Acta Pharm Sin B. 2021. Peer-reviewed study
- Agrawal M, Saraf S, Saraf S, et al. Nose-to-brain drug delivery: An update on clinical challenges and progress towards approval of anti-Alzheimer drugs. J Control Release. 2018. Peer-reviewed study
- Parida P, Prusty AK, Patro SK, et al. Current Advancements on Oral Protein and Peptide Drug Delivery Approaches to Bioavailability: Extensive Review on Patents. Recent Adv Drug Deliv Formul. 2024. Peer-reviewed study