system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Why do SSRIs take up to 2 weeks to kick in, but only 2-3 days to wear off?
gpt
Imagine an empty swimming pool being filled with a hose.   To be allowed to dive, you must fill the pool to the 8 foot mark, so you put a plug in the drain. It takes many hours to fill up 8 feet of water. The water level needs to rise 8 feet, to reach the 'effective level'.

It's now 8' 1".

Someone removed the drain plug. The water level only needs to fall more than an inch before it goes below the 'effective level, where it's not allowed to dive.

Also, the drain is letting water out faster than the hose brings water in. So it only takes a few minutes before it's not safe to dive again.

In this analogy, the SSR inhibitor is the drain plug.