- Shop GNC for vitamins, supplements, minerals, herbs, sports nutrition, diet and energy, and health and beauty products at gnc.com.www.gnc.com
- Amazon.com: Source Naturals L-Tryptophan 500mg, 120 Capsules: Tommy James: Health & Personal Care.www.amazon.com/Source-Naturals-L-Tryptophan-500mg-Capsules/dp/B000GFSVS2
- Tryptophan is an essential amino acid that must be obtained from foods, such as milk. It is a precursor of the neurotransmitter serotonin.www.iherb.com/L-Tryptophan