L-Tryptophan
An essential amino acid. Studied in combination with alpha-casozepine in anxious dogs and cats.
Why this grade: For dogs, two randomised placebo-controlled trials with opposite results: Kato et al. 2012 found lower stress scores on a tryptophan-rich diet, Bosch et al. 2009 found no difference in privately owned dogs. A knowledge summary in Veterinary Evidence (2024) rates this as moderate evidence. Comparable studies in cats are missing.
„amino acid, precursor of serotonin“
Reference amount per kg per day
Products containing L-Tryptophan
Why there is no amount here
The trials, Bosch et al. 2009 and Kato et al. 2012, added tryptophan to the food rather than giving a daily amount per kg of body weight. On top of that, every complete food already has to contain tryptophan as a nutrient. A range here would measure whether a product is dosed like other products, not whether the amount does anything.