Why are these almost all injections? What is wrong with capsules?

I would very much rather not inject anything. Capsules exist and are sold. Are they useless, or is the injection preference just habit?

Not habit. Your digestive system is specifically, evolutionarily good at destroying peptides, because peptides are food.

Two obstacles. First, proteases in the stomach and small intestine — enzymes whose entire function is cutting amino acid chains apart. Second, the gut wall, which is built to let small molecules through and hold large ones back, and most of these are on the wrong side of that.

So an oral peptide has to survive being digested and then get absorbed anyway. Most do neither.

It is worth saying it is not impossible, because the exception is instructive.

Oral semaglutide exists and is a licensed product. Getting there required co-formulating it with an absorption enhancer, a specific dosing procedure with water and a fasting window, and even then the bioavailability is low single-figure percent — the tablet contains many times more drug than an injection because most of it will not make it.

That is what solving this problem looks like: pharmaceutical formulation science and a lot of money, for one molecule. A capsule with peptide powder in it has not done any of that.

So when you see BPC-157 sold in capsules, the claim is usually that it acts locally on the gut and does not need to be absorbed. That claim is at least coherent for a gut effect. For a tendon, it requires the peptide to reach the tendon, and nothing about a capsule gets it there.

That is a clear answer and not the one I wanted. The capsule version is a different product wearing the same name.

The same problem is why topical peptide skincare is such a mess of claims. Skin is also a barrier that keeps large molecules out — that is its job.

GHK-Cu is the one with actual human studies behind it, and even there the interesting question is how much crosses and what it does on the way. Most serum marketing skips straight past that to the outcome.

Well, that has saved me some money. Thank you both.