That’s exactly what some biological drugs are too - peptides!
And peptides are just short chains of amino acids. Almost all the other biological drugs are just longer chains of amino acids - antibodies, enzymes, antigens, some hormones, and others.
Derek is right that the safety risks are exponentially higher when you inject peptides - you basically skip a bunch of protective mechanisms like enzymes that quickly break them down if taken orally or routes.
As a former R&D scientist there is no way I’d inject any peptide that hasn’t at least gone through a phase 1 safety study in humans. Otherwise you have no idea what it could be doing to your body.
A good example was a drug that was quickly pulled from market for causing fatal anaphylactic reactions. It wasn’t even caught in the clinical trials!
At the same time, I think people have the right to take whatever substance they want. But I worry a lot of people aren’t aware of the risks.