system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is LSD illegal?
gpt
The basic philosophy of US drug laws is that *all* drugs should be illegal unless they serve a definite medical purpose.  Any use that's not for some medical condition is considered "abuse" under this framework - it doesn't necessarily need to be harmful or addictive.

There's no room in this legal framework for legal recreational drugs.  The exceptions - alcohol, tobacco & caffeine - are, for purposes of the law, "not drugs" due to historic reasons.

Since there's no medical use for LSD, it's not legal.