Apparently, there is no causal link between low serotonin and depression.
SSRI antidepressants are not good for you. They have no positive effects, and they don’t make your depression any better. If you are on them because a doctor told you they would help your depression, he or she was wrong and you should stop taking them.
I've been saying this for, oh, only twenty years or so. It was obvious that they didn't work - depressed people clearly weren't improving with them. Studies demonstrating lack of long term efficacy were available back in the 90s at least, I believe. In sharp contrast to MDMA therapy, which was showing robust results - significant, sustained improvement - with just a few treatments in conjunction with trained psychotherapists.
Several years back I was feeling pretty depressed and overwhelmed. This was in grad school during a particularly heavy time. My university offered free therapy sessions, following a rash of student suicides. I consider psychiatrists to be witch doctors but I figured, eh, it's free.
After twenty minutes of explaining what was getting to me, she said, "You seem to have a lot of insight into your condition ... I think I know what you'll say, but I'm required to ask. Would you like a prescription?"
Laughed in her face and walked out.
Whole industry is a scam.
A horrible counter-thought: Serotonin has been consistently ben useful on treating psychopathy and other anti-social behaviors like reactive (vulnerability-induced sociopathic) aggression and violence. It is the neurotransmitter of "being in the right place within the hierarchy", and so many job-fit people are not part of the gentry or aristocratic classes (the upper-middle and upper classes). They are the ones most likely to act like "counter-elite" "revolutionary" types. Those management and professional seats are now over by narcissists who take over those positions. The opposite of low serotonin is pedophilic risk (see SLC6A4 mutation for some pointer). In times where the underqualified gets on high-up positions, CSO among the upper class is predicted to increase. Turchin's wellbeing index is tied to the amount of psychos, whilst "elite overproduction" is tied to the amount of nonces.
A secondary thought: nowadays it is understood that Dopamine (anticipation) and GABA (forgiveness) controls how mania and depression are controlled. Everything from diet and exercise, to MDMA/LSD/THC, to socializing and shamanic therapy... most things work. Why is it so difficult for HR departments and management to understand this?