Serotonin and its receptors are an integral part of many physiological functions in the nervous, endocrine, and gastrointestinal systems; serotonin is important for regulating mood and sleep-wake function. 

Taurine is a neuroprotective amino acid that provides antioxidant protection. It demonstrates GABA-A agonist activity, which increases the amount of GABA in the brain; GABA is the primary inhibitory neurotransmitter in the brain important for calm and sleep. 

L-theanine is an amino acid that acts as a glutamate receptor antagonist, which blocks glutamatergic signaling, the underlying mechanism relating to anxiousness and stress. In a randomized, double-blind, placebo-controlled study, L-theanine was shown to significantly reduce stress. 

5-HTP crosses the blood-brain barrier and is a precursor to serotonin and melatonin. In a randomized, double-blind study, 5-HTP was shown to significantly improve mood. 

Active forms of vitamin B6, folate, B12, and C are important for serotonin synthesis.