Biggest example of this risk aversion is the peptide craze going on (the most famous of which are GLP-1 antagonists). It's pretty much a wild west where people read a low-sample animal study, and buy a drug that's "for research only, not for human consumption" off of a compounding pharmacy in China.
Few human studies because even if you have willing and enthusiastic volunteers it's too expensive and creates legal liability. And the FDA cannot approve it without a high bar of evidence (for effective treatment and low risk) and costly, time consuming reviews. Because of this, there is a black market for the things and people are basically being their own test subjects.