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What you‘ll find in this article:

What is L-tryptophan and why it comes up

L-tryptophan is a naturally occurring amino acid your dog gets from food. The body, your dog’s and ours too, uses it to make serotonin, aka the “feel good” hormone, a messenger involved in mood and stress response. Clinical interest comes from human and animal research that links dietary L-tryptophan to behaviour, where it has been studied for its potential to influence anxiety-related behaviour, alongside other factors that regulate serotonin levels (Fan et al. 2023).

Does L-tryptophan help anxious dogs

Current dog studies are small and give mixed results. One study found no significant effect on anxiety, another found that owners noticed ‘lower’ anxiety scores, but stress-hormone measures did not shift (Veterinary Evidence Summary, 2024). There is, however, one important detail from research: it’s not just the amount of L-tryptophan that matters, but how it balances with other amino acids in the diet. They all use the same “bus” to get into the brain, so if there are too many of the others, tryptophan can get crowded out. This may be why some studies show mixed results (Templeman et al., 2018). A blend that combines L-tryptophan with other calming ingredients can make sense, because it doesn’t rely on this pathway alone.

Where it fits in a doggy calm plan

L-tryptophan sits in the “adjunct” bucket, alongside training, environment tweaks and, when appropriate, veterinary-prescribed therapies or behavioural plans. Nutrition should be part of a plan that’s tailored to the individual dog, and not used in isolation. As with all supplements, dietary and lifestyle changes, small measures stack up to something much bigger, and are not stand-alone fixes. (WSAVA Global Nutrition Guidelines).

Choosing a product, reading the label and when to check with your vet

That being said, look for supplements that contain clear per-scoop amounts, named actives and reliable batch information so you can make sure products are in date. Keep other changes to a minimum whilst you trial something new, that way it’s easier to isolate any observed changes and make adjustments where necessary. 

Speak to your vet if your dog is on behaviour medications or has a medical condition. Keep notes on appetite and stool quality during a trial, and use a monitoring score (your own interpretation is fine, you spend the most time with them!) to track progress. Owner scores often improve whilst physiological markers do not, so consistent, repeatable observations really do matter (Veterinary Evidence, 2024).