Tryptophan and melatonin as treatments

Tryptophan is the essential amino acid precursor to the monoamine neurotransmitter serotonin, which is associated with several brain functions such as modulating mood, cognition, vomiting, impulsivity as well as sleep and circadian rhythm. The latter is due to serotonin's role as a precursor for melatonin—a light-sensitive hormone underlying the complex sleep–wake cycles in vertebrates. Melatonin and tryptophan supplementation have proven useful treatments in certain contexts, including depression, traumatic brain injury, delayed sleep phase syndrome, delirium, childhood parasomnias and insomnia. Background information and physiology of these two biomolecules are provided followed by investigation of the evidence for their clinical significance.