You need lots of test subjects, control groups, "blind tests". And someone need to manage everything so it can be done in a controlled environment.

It's really not as simple as just having a bunch of people testing it. You introduce placebo that way. Which the "official" process eliminates through their control groups and by injecting nothing but saline solutions while telling you it's the real deal.

Or rather. You are made aware you may or may not recieve the real deal. You just don't know.

Those side effects are not common. Because they would be unacceptable and "eliminated" before moving on to human trials. I put that in quotation marks because there's probably a non zero risk. Just astronomically small.

Example. People have been observed getting drunk on non alcoholic drinks. But they're not really drunk, they just think they are.