I have never taken anything like that before but I will supplement with Creatine for a couple months here and there.
One guy I work with was telling me I should look into peptides, but I don't feel like researching them when I have no intention of using them.
He swears it strengthened his immune system. He was suffering from a severe autoimmune disease that manifests itself as extreme athritis. It was really fucking him up. He was in his thirties and couldn't even get off the couch, he as was totally decrepit. He lost all his muscle mass, etc.
Now his lifting heavy and he is fit and he swears he has peptides to thank for it, and tells me they are either natural or close to natural. Again, I have not researched it.