system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can't drug users just ingest/inject dopamine instead?

I feel dumb asking but don't drugs eventually turn into dopamine, or deal with dopamine receptors, anyways?
gpt
Well for starters dopamine is a neurotransmitter, it's not something that travels through the bloodstream, and likely wouldn't be able to pass through the blood-brain barrier either (a sort of biological gate-keeper for the brain).