Acetyltryptophan, L- functions readily as a component of the food in place of the free amino acid. Acetyltryptophan, L- is a neurokinin-1 receptor antagonist. It significantly improved motor and cognitive outcomes in models of Parkinson’s diseases, as well as reduced brain edema and axonal injury in experimental traumatic brain injury and stroke. It is a potent therapeutic agent for the treatment of amyotrophic lateral sclerosis.