--- title: "L-Tryptophan for Dogs and Cats | Petz Park" description: "L-Tryptophan — active ingredient in Petz Park supplements. L-Tryptophan in Petz Park supplements. Learn about the mechanism, evidence, and safety." lang: en json-ld: | [ { "@context": "https://schema.org", "@type": "BreadcrumbList", "itemListElement": [ { "@type": "ListItem", "position": 1, "name": "Home", "item": "https://knowledge.petzpark.com.au" }, { "@type": "ListItem", "position": 2, "name": "Ingredients", "item": "https://knowledge.petzpark.com.au/ingredients" }, { "@type": "ListItem", "position": 3, "name": "L-Tryptophan", "item": "https://knowledge.petzpark.com.au/ingredients/l-tryptophan" } ] }, { "@context": "https://schema.org", "@type": "MedicalWebPage", "name": "L-Tryptophan", "description": "L-Tryptophan for Dogs and Cats | Petz Park", "url": "https://knowledge.petzpark.com.au/ingredients/l-tryptophan", "about": { "@type": "Substance", "name": "L-Tryptophan" }, "publisher": { "@type": "Organization", "name": "Petz Park", "url": "https://petzpark.com.au" } }, { "@context": "https://schema.org", "@type": "ItemList", "name": "Products containing L-Tryptophan", "itemListElement": [ { "@type": "ListItem", "position": 1, "url": "https://knowledge.petzpark.com.au/dogs/products/stress-anxiety-for-dogs", "name": "Stress and Anxiety for Dogs" } ] } ] --- [![Petz Park logo](/images/petz-park-logo.png)](https://www.petzpark.com.au/?utm_source=knowledgecentre&utm_medium=ingredient_article&utm_campaign=l_tryptophan&utm_content=navigation) [Home](/) [Dogs](/dogs) [Cats](/cats) [Products](/products)[Ingredients](/ingredients)[Comparisons](/comparisons)[FAQs](/faqs)[Trust & Proof](/trust) About [Visit Store](https://petzpark.com.au/?utm_source=knowledgecentre&utm_medium=ingredient_article&utm_campaign=l_tryptophan&utm_content=header_cta) 1. [Home](/) 3. [Ingredients](/ingredients) 5. L-Tryptophan # L-Tryptophan L-Tryptophan is an essential amino acid that cannot be synthesised by mammals and must be obtained through diet. It is the sole dietary precursor to serotonin, melatonin and several other neuroactive compounds. It is one of the few calming supplement ingredients with published clinical evidence specifically in dogs. ## Mechanism of Action After crossing the blood-brain barrier via the large neutral amino acid transporter, L-Tryptophan is converted to 5-hydroxytryptophan (5-HTP) by tryptophan hydroxylase, then to serotonin by aromatic amino acid decarboxylase. Serotonin is the primary neurotransmitter governing mood, anxiety, aggression and sleep quality. L-Tryptophan is also the precursor to melatonin through sequential enzymatic steps in the pineal gland, making it relevant to sleep disruption associated with anxiety or ageing. Dietary protein competes with tryptophan for the blood-brain barrier transporter, which is why the ratio of tryptophan to other large neutral amino acids in the diet affects central serotonin synthesis. ## Evidence Summary L-Tryptophan has been studied directly in dogs. A study by DeNapoli et al (2000, Journal of the American Veterinary Medical Association) found that tryptophan supplementation combined with a low-protein diet reduced dominance aggression scores in dogs. A further study by Bosch et al (2009, Journal of Nutritional Science) found tryptophan supplementation reduced anxiety-related behaviours in dogs exposed to standardised stressors. These are among the only randomised dog-specific studies for any ingredient in the Stress and Anxiety formula. ## In Petz Park Products Stress and Anxiety for Dogs: L-Tryptophan 85mg per scoop. Note: L-Tryptophan is also present in the Stress and Anxiety for Cats formula. The cat formula is currently being updated and the confirmed dose will be added here once finalised. ## Safety and Considerations L-Tryptophan is safe at supplemental doses in dogs and cats. It should be used with caution in animals on serotonergic medications including SSRIs, MAOIs or tramadol due to the theoretical risk of serotonin syndrome at pharmacological doses. At supplemental doses the risk is low but veterinary oversight is recommended in any animal on these drug classes. ## Used in These Products Dog Products - [Stress and Anxiety for Dogs](/dogs/products/stress-anxiety-for-dogs) ## Helps With These Concerns Dog Health - [Anxiety and Stress in Dogs](/dogs/anxiety) Cat Health - [Anxiety and Stress in Cats](/cats/anxiety) [Back to Ingredients](/ingredients) Explore the Knowledge Centre - [All Ingredients](/ingredients) - [Dog Supplements](/dogs) - [Cat Supplements](/cats) - [Knowledge Centre Home](/) ![Petz Park](/images/petz-park-logo.png) Australian-made pet supplements for dogs and cats. ### Explore - [Home](/) - [Dogs](/dogs) - [Cats](/cats) - [Products](/products) - [Ingredients](/ingredients) - [Comparisons](/comparisons) - [FAQs](/faqs) - [About](/about) - [Trust & Proof](/trust) ### Dog Health - [Joint Health for Dogs](/dogs/joint-health) - [General Health and Vitality for Dogs](/dogs/general-health-vitality) - [Urinary and Kidney Health in Dogs](/dogs/urinary-kidney-health) - [Probiotics for Dogs](/dogs/probiotics) - [Liver Health for Dogs](/dogs/liver-health) - [Skin, Coat and Allergies in Dogs](/dogs/skin-coat-allergies) - [Brain and Cognitive Health in Dogs](/dogs/brain-cognitive-health) - [Anxiety and Stress in Dogs](/dogs/anxiety) - [Eye Health for Dogs](/dogs/eye-health) - [Dental Health for Dogs](/dogs/dental-health) - [Senior Dog Health](/dogs/senior-dog-health) - [Immune and Seasonal Health for Dogs](/dogs/immune-seasonal-health) ### Cat Health - [Joint Health for Cats](/cats/joint-health) - [Anxiety and Stress in Cats](/cats/anxiety) - [Dental Health for Cats](/cats/dental-health) - [Liver Health for Cats](/cats/liver-health) - [Skin, Coat and Allergies in Cats](/cats/skin-coat-allergies) - [General Health and Vitality for Cats](/cats/general-health-vitality) - [Urinary and Kidney Health in Cats](/cats/urinary-kidney-health) - [Eye Health for Cats](/cats/eye-health) - [Probiotics for Cats](/cats/probiotics) ### Contact - [petzpark.com.au](https://petzpark.com.au/?utm_source=knowledgecentre&utm_medium=ingredient_article&utm_campaign=l_tryptophan&utm_content=navigation) [Instagram](https://www.instagram.com/petzpark "Instagram")[Facebook](https://www.facebook.com/petzpark "Facebook")[TikTok](https://www.tiktok.com/@petzpark "TikTok") © 2026 Petz Park. 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