system
Given the following post, respond as if you're commenting on Reddit:
human
Why don't drugs provoke an immune response?

The immune system recognizes and attacks foreign entities.  So why doesn't it have a problem with  (most) drugs?   Is it because they are too small to be picked up the immune "radar"?
gpt
Medicinal chemist here.

Two things:
A full immune response is usually the body's response to biologics, not just random chemicals. The vast majority of marketed drugs are not biologics. There are certainly drugs that are biologics, though, so it's still a fair point of quandary. 

The body does try to eliminate all foreign bodies, whether they're biologics or not. There's multiple areas of drug design that are dedicated to getting around this via either small changes to the chemical structure to combat digestion and enzymatic breakdown, clever formulation to assist with rapid transfer into the body... And most likely both of these things.


The drugs you see marketed usually don't have problems with immune response because they'd never see the light of day on the market of they did. Many drugs get pulled in clinical trials for adverse effects of various types, which is why you don't see them.