L-theanine and alpha-casozepine for anxiety in dogs and cats
L-theanine and alpha-casozepine for anxiety in dogs and cats: what does research say about efficacy and safety?
Short & honest
Alpha-casozepine and L-theanine show limited evidence of efficacy for anxiety in dogs and cats (grade C); studies are small or methodologically limited, and these supplements do not replace veterinary behavioural diagnosis.
Safety assessment: Safe when used correctly
Veterinary review not yet completed
This page is awaiting review by a registered veterinary surgeon. Until then, treat the text as education based on the sources listed — not as a verified veterinary judgement.
What are alpha-casozepine and L-theanine?
Alpha-casozepine is a bioactive decapeptide released during the digestion of alpha-s1-casein, a protein in cow's milk. It binds to GABA-A receptors — the same receptors targeted by benzodiazepines — but without sedative side effects. Commercially available under brand names such as Zylkene.
L-theanine is an amino acid naturally occurring in green tea. It is suggested to have a calming effect via glutamate and GABA pathways. Available for companion animals as Anxitane and in combination preparations.
What are they used for?
Both substances are recommended for situation-specific anxiety in dogs and cats, such as:
- Anxiety regarding veterinary visits or transport
- Sound phobia (thunderstorms, fireworks)
- Separation anxiety (mild to moderate)
- Adjustment problems in new environments
What does the research say?
Alpha-casozepine in dogs
A double-blind, placebo-controlled RCT from 2025 showed that alpha-casozepine significantly reduced stress behaviour in dogs during veterinary visits compared to placebo [2]. An older comparative study found similar efficacy to selegiline (an MAO inhibitor used for anxiety disorders in dogs) over a period of 56 days [1].
These results are encouraging, but they involve only two studies, one of which is a narrative review. The research base is too narrow to make strong statements.
Alpha-casozepine in cats
An RCT in 24 cats with a diet supplemented with alpha-casozepine and L-tryptophan showed a reduction in anxiety reactions in an unfamiliar environment. However, there was no significant effect during direct confrontation with an unfamiliar person [3]. The small sample size and the combination of multiple ingredients make it difficult to determine exactly what is effective.
L-theanine in dogs
Pilot studies in dogs with sound phobia suggest improvement, but exclusively in combination with behaviour therapy [4]. The studies are small and have methodological limitations: among other things, adequate blinding is lacking. The independent effect of L-theanine is therefore difficult to assess.
Safety
Both supplements are considered safe when used at the recommended dose. They are not sedating, which is an advantage compared to anxiolytics. Caution is advised with alpha-casozepine (derived from milk casein) in animals with a cow's milk allergy.
Neither of these supplements is suitable as a replacement for veterinary behavioural diagnostics or pharmacotherapy in severe anxiety disorders. Professional guidance is necessary in cases of persistent or escalating anxiety.
Practical considerations
| Aspect | Alpha-casozepine | L-theanine |
|---|---|---|
| Evidence quality | Weak (C) — 1 RCT + comparative | Weak (C) — small pilot studies |
| Sedating | No | No |
| Species studied | Dog, cat | Dog |
| Combined with behaviour therapy? | Not required in studies | Yes, in available studies |
Always consult the veterinary surgeon before starting a supplement, especially in animals already receiving medication or in cases of severe anxiety problems.
Why this verdict?
The evidence consists of a few small RCTs and pilot studies; for alpha-casozepine, one double-blind RCT is available (2025), but the research base remains narrow. L-theanine studies lack adequate blinding and were conducted in combination with behaviour therapy, leaving the independent effect unclear. Grade C: weak evidence — positive signals, but insufficient robust replication.
Interactions with medication
- Caution when combining with benzodiazepines or other GABAergic agents (alpha-casozepine acts on the same receptor system; additive effect not excluded)
- Selegiline: comparative studies show similar efficacy; combination not investigated for safety [1]
Legal status (Netherlands)
Freely available as a dietary supplement or dietetic preparation; not registered as a medicinal product in the Netherlands. Zylkene falls under dietetic foods for particular medical purposes (veterinary dietetic products).
Sources
- [1] Effects of alpha-casozepine (Zylkene) versus selegiline hydrochloride on anxiety disorders in dogs. Journal of Veterinary Behavior / ScienceDirect, 2008. Narrative review source ↗
- [2] Efficacy of alpha-casozepine in reducing dogs' anxiety during veterinary visits: a randomized, fully-blinded, placebo-controlled study. Journal of Veterinary Behavior / ScienceDirect, 2025. RCT source ↗
- [3] Therapeutic effects of an alpha-casozepine and L-tryptophan supplemented diet on fear and anxiety in the cat. Frontiers in Veterinary Science / PMC, 2017. RCT source ↗
- [4] An open-label prospective study of the use of L-theanine (Anxitane) in storm-sensitive client-owned dogs. Journal of Veterinary Behavior / ScienceDirect, 2015. Narrative review source ↗
Questions about this substance for your animal?
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