[safety1st]

This one is really interesting, thanks. I think it's the closest any mentioned substance comes to passing the "creatine test" (for whatever that test is worth; I just made it up).

(A) The body of research is, in general, large and uncontroversial.

(B) The safety profile is good. The benefits for diabetics are certainly large. Probably no drug has been studied for anti-aging effects as extensively as creatine has been for fitness applications, so I'm not sure anything can fulfill that criteria. But it seems like the present research on metformin supports a variety of positive effects for non-diabetics with more on the way.

(C) I wouldn't know whether the majority of people who are serious about anti-aging use it but it does get mentioned a lot.

Pretty positive endorsement overall!