system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If it takes up to 6 weeks for an antidepressant to work its way theough the blood-brain barrier, how come it only takes an aspirin 10 minutes to start working?

And many other drugs too ...
gpt
Because it doesn't take weeks to cross the blood brain barrier. It gets there in mins to hours like everything else, But ssri's take weeks to change the way your brain works. Which is when you will start feeling them "work".