A peptide is food to a protease
The digestive tract is very good at taking chains of amino acids apart. That is literally its job. A peptide swallowed as-is meets stomach acid first and a wall of proteolytic enzymes second, and most of them do not come out the other side intact enough to be worth measuring.
There are two ways around it. Either the sequence is unusually resistant, or the target sits in the gut itself, so degradation on the way to the bloodstream is beside the point. Both of the products on this page fall into one of those two categories.
Anyone offering you a long list of oral peptides is either using enteric coating claims they cannot support, or is not being straight with you about what happens after the capsule dissolves.
What decides whether oral works
- Chain length, shorter sequences fare better
- Whether the target is in the gut or past it
- Resistance to proteolytic cleavage
- Whether the literature measured anything at all after oral use
Research context only. This is not a statement about effects in people.
Capsules and the solvent
Two capsule products, plus the bacteriostatic water that every reconstitution step needs.
Judging an oral claim
How to tell a defensible capsule from a marketing one, and what the paperwork does not cover.
Peptide capsules are the format where the gap between the container and the claim is widest. A certificate of analysis describes the material at the point it was filled: which compound is present, how pure it is, which batch it belongs to. It says nothing about what remains intact once the shell dissolves, because that is a question for pharmacokinetic work rather than for an analytical laboratory. Both kinds of evidence are useful; conflating them is how an ordinary capsule acquires an extraordinary reputation.
The two products on this page are here for the two defensible reasons. KPV is three residues long and its research question sits in the gut itself, so degradation on the way to circulation matters far less than it normally would, the KPV page sets that argument out in full. Dihexa is not really a peptide at all but a small molecule with peptide ancestry, built from the outset to survive metabolism, which is why the dihexa page spends as long on that design history as on the mechanism.
Anyone weighing a supplier’s oral range against that standard has a straightforward test: ask what makes each sequence an exception. A supplier who cannot answer for a specific compound is selling the format rather than the molecule, and the published work on oral peptide bioavailability is where the exceptions are actually catalogued. The literature is small for a reason, and a long catalogue is not evidence that the reason has gone away.
Related reading
Where these compounds sit in the wider literature.
About the oral format
What people ask about capsules specifically.