Asklemmy

Yes and no (and a disclaimer: I'm only a nurse). There are several herbs that work similarly to Selective Serotonin Reuptake Inhibitors (SSRIs). The issue being that they therefore have the same risks as SSRIs: the two big ones being serotonin syndrome (all your vital signs shoot up until it kills you) and less dangerously but not really less unpleasantly, mania and/or psychosis if that's something your genetics have predisposed you do. These are both a lot less likely with herbs than medications because they're much weaker, but it's still possible, and especially if you take them WITH an SSRI. There are also some recreational drugs (shrooms, lsd, MDMA) that can cause serotonin syndrome when you take too much or take them with other serotonin boosting medications. I don't recommend you play with this kind of thing without medical supervision. I actually had one of our severe bipolar cases come back to us high as tits because they swapped their mood stabilizer for a serotonergic herb, it was a mess.

Anyway the big three are St John's Wort, Ashwaganda, and Moringa. L-tryptophan is also known to boost serotonin, but that's just because it's one of the building blocks your body needs to make it. Melatonin can also help your serotonin because it and serotonin turn into each other as part of the cycle of your circadian rhythm but be careful not to take too much of it because you'll start having extremely bizarre nightmares.

But like I said, you're better off talking to a doctor about this before you find out you've been bipolar II this entire time when the herbs you bought on Amazon turn it into bipolar I and you spend a month in a psych ward thinking your you're the second coming of Christ and putting chess pieces in your ass to fight the demons.