A swallowed peptide meets digestive enzymes first, and they break it into pieces. In a human study a dose of GHRP-6 taken by mouth, ten times larger than the nasal dose, moved neither growth hormone nor ACTH nor cortisol. The same molecule given into the nose raised growth hormone for the whole night. Below is what was measured for four routes of administration, and why the vials in our shop are for dissolving, not for drinking.
Why the digestive tract is hard on a peptide
A peptide is built from amino acids joined the same way as protein from a meal. Proteolytic enzymes therefore treat it as food and break it down. The second obstacle is the low permeability of the gut wall to molecules of this size. Both limitations are named in a 2024 review of semaglutide pharmacokinetics, explaining why the oral form needed a technology of its own.
This shapes the whole peptide market. Injection is the default route, and every other route has to prove that something actually reaches the blood.
The study that compared three routes for the same molecule
In 1999 the Journal of Neuroendocrinology published a paper on GHRP-6 in healthy young men. It compared enteric capsules swallowed at 9 pm with nasal and sublingual administration at 10.45 pm, each against placebo. The oral dose was 300 micrograms per kilogram of body weight, and the other two were 30 micrograms per kilogram each.
| Route | Dose | What changed |
|---|---|---|
| Oral, enteric capsule | 300 micrograms per kilogram | growth hormone, ACTH and cortisol unchanged |
| Sublingual | 30 micrograms per kilogram | a tendency towards higher growth hormone in the first half of the night |
| Nasal | 30 micrograms per kilogram | a significant rise in growth hormone throughout the night |
The authors word their conclusion carefully, and we give it exactly that way: the effect depends on the dose, the timing and the route. An oral dose ten times larger did not reproduce what a small nasal dose did.
The nose does better, but not for every molecule
A separate paper in Xenobiotica from 1998 measured nasal absorption in rats for five secretagogues at once. The nasal bioavailability of ipamorelin was estimated at about 20 per cent, and that of GHRP-2 and two experimental molecules at about 50 per cent. GHRP-6 was absorbed less well than those.
The same study found a difference in elimination. Ipamorelin left the body mainly in urine, while GHRP-6 left mostly in bile, with five times higher plasma clearance. These were animal studies, so we do not carry the numbers over to humans. The molecules themselves are compared in the guide to GHRP-2, GHRP-6, ipamorelin and hexarelin.
Oral semaglutide: the cost of getting through the gut
Semaglutide is the only GLP-1 analogue available in both forms, for injection and for swallowing. The 2024 review gives the bioavailability of the oral form as 0.8 per cent under the recommended conditions of intake. Absorption is faster than after injection but much more variable.
The half-life stays the same regardless of route, at about a week. Yet the oral form is taken daily and the injectable form once a week. Our shop stocks only vials of lyophilised powder, as the semaglutide page shows.
Subcutaneous or intramuscular
With injectable peptides there is still the choice of layer. A study in Fertility and Sterility from 1991 gave 5000 units of chorionic gonadotropin to twenty-four healthy men, half subcutaneously and half intramuscularly. After subcutaneous administration the peak concentration came later and the half-life was longer.
The testosterone, LH and FSH response was identical in both groups. The authors considered the subcutaneous route equally effective. Figures for the other compounds are gathered in the guide to peptide half-lives.
What this means for a vial from our shop
Every item in the catalogue is lyophilised powder, to be dissolved before use. We do not sell capsules, drops or nasal sprays, because for these molecules there are no data that would justify such forms. The only exception in terms of form is ready-made pens with solution, described separately.
The peptide where the question of route comes up most often is BPC-157. That is covered in the guide to BPC-157 oral or injected. Dissolving itself is described in the guide to reconstitution with bacteriostatic water, and the full range is on the price list.
Frequently asked questions
Can a peptide be swallowed?
Digestive enzymes break it down like protein from a meal. In the GHRP-6 study the oral dose changed none of the measured hormones.
Does nasal administration work?
For GHRP-6, yes: a small nasal dose raised growth hormone for the whole night. Bioavailability, however, depends on the molecule.
Why is oral semaglutide taken every day?
Its bioavailability is 0.8 per cent, and absorption is more variable than after injection.
Subcutaneous or intramuscular?
In the HCG study both routes gave the same hormonal response, although the concentration curve differed over time.
Do you sell peptides in capsules?
No. Every item is lyophilised powder in a vial, meant to be dissolved.
Sources
- Frieboes RM, Murck H, Antonijevic IA, Steiger A. Effects of growth hormone-releasing peptide-6 on the nocturnal secretion of GH, ACTH and cortisol and on the sleep EEG in man: role of routes of administration. Journal of Neuroendocrinology, 1999, 11(6): 473-478. https://doi.org/10.1046/j.1365-2826.1999.00364.x
- Johansen PB, Hansen KT, Andersen JV, Johansen NL. Pharmacokinetic evaluation of ipamorelin and other peptidyl growth hormone secretagogues with emphasis on nasal absorption. Xenobiotica, 1998, 28(11): 1083-1092. https://doi.org/10.1080/004982598238976
- Yang XD, Yang YY. Clinical Pharmacokinetics of Semaglutide: A Systematic Review. Drug Design, Development and Therapy, 2024, 18: 2555-2570. https://doi.org/10.2147/DDDT.S470826
- Saal W, Glowania HJ, Hengst W, Happ J. Pharmacodynamics and pharmacokinetics after subcutaneous and intramuscular injection of human chorionic gonadotropin. Fertility and Sterility, 1991, 56(2): 225-229. https://pubmed.ncbi.nlm.nih.gov/1712735/