Tryptophan

It is used in calming formulas for stressed cats, cats moving to a new home and multi-cat households, but the evidence for this effect in cats is limited for now.

Tryptophan is an essential amino acid for cats, found in meat and eggs. FDA lists tryptophane (L- and DL-forms) as GRAS for animal feed under good manufacturing or feeding practice (21 CFR 582.5915). AAFCO also sets an upper limit for cat food. If your cat takes behavior medication or has a medical condition, ask your veterinarian before choosing a food with added tryptophan.

Source: govinfo.gov

Tryptophan is added for two reasons. Cats need it to build proteins, and the body turns it into serotonin, a brain chemical tied to mood and sleep. Calming cat foods use extra tryptophan for that second reason. Evidence for that effect in cats is still limited.

Not in useful amounts. The Merck Veterinary Manual says cats cannot make substantial niacin from tryptophan, so they must get all their niacin from food. Dogs and people can turn some tryptophan into niacin. That is one reason cat foods carry added niacin even when they contain plenty of tryptophan.

Source: merckvetmanual.com

Yes. AAFCO cat food nutrient profiles cap tryptophan at 1.7% of dry matter. The minimums are 0.16% for adult maintenance and 0.25% for growth and reproduction. Calming foods add tryptophan but still have to stay under that ceiling to meet AAFCO profiles. Tryptophan supplements given on top of food are a separate matter for your veterinarian.

Source: aafco.org

Pettings gives tryptophan 4 out of 5 and lists it as an amino acid. It appears on 9 of the 149 dry cat foods we list. The score is for the ingredient itself and does not rate any calming claim. Each food's page shows how it scores overall.