I think the 5HTP just assures you have adequate precursors to make serotonin from. Adequate serotonin is needed for good sleep (but is not sufficient for). Adequate serotonin is also needed for good mood, so taking the 5HTP may help with both mood and sleep.I've never really known whether to believe it really helps with serotonin, but that's how the thinking goes, and it looks like it does help several who have posted here. Hope it works for you too!