It's back, and better than ever! L-Tryptophan is a precursor to serotonin, and it's powerfully effective when used properly. By supporting serotonin levels, L-tryptophan not only helps us fall asleep and stay asleep, but it also promotes mental health and provides dietary support against nervousness and tension. TryptoPure L-Tryptophan from Swanson Ultra is the purest pharmaceutical-grade tryptophan on the world market. It's produced through a natural fermentation process from a vegetarian source, using the most precise standards for safety and quality assurance.