system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5, how do SSRI’s work for anxiety disorders?
gpt
Neuroscientist here: the real answer is "we have no idea".

We have no idea how SSRIs work to treat depression, either. Anyone who says otherwise doesn't know what they're talking about. 

We know what the immediate chemical effects of SSRIs are... they decrease reuptake of serotonin (reabsorption by the brain cell that released it). But we're not even 100% sure when that results in more serotonin release vs. less! Many serotonin releasing neurons have their own serotonin receptors that inhibit further serotonin release, and SSRIs will cause those to become more stimulated. Also, we know that the effects of SSRIs on serotonin take only a couple hours, but we also know that the antidepressant effects take a few weeks to appear, which means that whatever is happening isn't directly a result of increased serotonin release. It probably has to do with other neurons adapting to the change in serotonin release, and that adaptation somehow leads to the antidepressant effect. 

Brains are really complicated. Anyone who gives you a simple explanation for something as complex as depression, like "serotonin = happiness, depression = not enough serotonin" is full of shit (neither of those things is remotely true).