Tryptophan is alpha-aminoacid that is used in the biosynthesis of proteins. It is essential aminoacid in humans, meaning the body cannot synthesize and it must be obtained from the diet. Tryptophan is a precursor of serotonin, and as such is sold over the counter in many countries as a dietary supplement for use as an antidepressant, anxiolytic and sleep aid, however application of tryptophan in these indications is not approved by FDA.

Methionine is an non-polar, aliphatic, essential α-amino acid that is used in the biosynthesis of proteins. High levels of methionine can be found in eggs, sesame seeds, Brazil nuts, fish, meats and some other plant seeds; methionine is also found in cereal grains. Most fruits and vegetables contain very little of it. Most legumes are also low in methionine. However, it is the combination of methionine and cystine which is considered for completeness of a protein. There is scientific evidence that restricting methionine consumption can increase lifespans in some animals. However, since methionine is an essential amino acid, it cannot be entirely removed from animals' diets without disease or death occurring over time. For example, rats fed a diet without methionine developed steatohepatitis (fatty liver), anemia and lost two thirds of their body weight over 5 weeks. Administration of methionine ameliorated the pathological consequences of methionine deprivation.

Methylcyclopentenolone (also known as methyl cyclopentenolone), a flavor compound that is used in the standard olfactory acuity test in patients with smell disorders.