system
Given the following post, respond as if you're commenting on Reddit:
human
Why does our brain have receptors for rare drugs that we wouldn't normally ever encounter, such as LSD?
gpt
The receptors aren't specifically for LSD. They're serving their own regular function related to normal brain behavior. Then, every once in a while a scientist will discover/invent a new chemical that happens to fit one or more of the existing receptor sites.