My favorite is Barry Marshall. He thought there was a connection between bacteria and ulcers, which was an unpopular opinion at the time. So he intentionally drank the offending bacteria, got sick as expected, and then people believed him.
More here, including (which I didn't know until now) cardiac catheterization.
Only on consenting adults who have the ability to reasonably reject the offer (so they're not forced into it for any reason, like money). The guy in the picture did it on babies, so… if you want to do it on yourself go ham, but that wouldn't be fair.
Animal experimentation is bad enough.
My understanding is that there were known, safe and effective alternatives already and that there is not guarantee what he did actually did anything or that it didn't cause some unknown harm.