I'd say human experimentation has become a big no-no. Pretty gnarly research has been done until the 70s, even 80s. Even for new drugs there are countless hoops to jump to get to the final human trials.

Right now you can study infected individuals just fine, but you can't go around inoculating people with diseases, even if they're volunteers.

One common pattern I've seen is that well known, old drugs, are either known to be ok for a pregnant woman, or not ok. But the bulk of drugs discovered since the 80s are "not advised unless necessary", "check with your doctor" and other variants of passing the hot potato.