Sleep latency in normal human subjects is significantly reduced by bedtime administration of the amino acid L-tryptophan. The reduction in sleep latency (approximately 50%) is significant even at a dose of 1 gm of L-tryptophan, which approximates the L-tryptophan content of 0.5 kg of meat. The electroencephalographic stages of sleep and the cycle of sleep are not significantly affected by low doses of L-tryptophan, but, at one or more of the higher doses (10 to 15 gm), there is a decrease in desynchronized sleep and an increase in slow-wave sleep.
Hartmann E, Cravens J. Hypnotic Effects of L-Tryptophan. Arch Gen Psychiatry. 1974;31(3):394-397. doi:10.1001/archpsyc.1974.01760150098014