system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does it take so long for mood stabilizing drugs such as antidepressants to work?
gpt
In the case of antidepressants, it's because their mechanism of action is neurogenesis in the hippocampus. This process takes roughly two weeks to have an effect on serotonin levels.  

The fact that antidepressants act via hippocampal neurogenesis is relatively recently discovered by science - within about the last ten years.