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What Zylkene is
Zylkene is based on alpha-casozepine, a peptide derived from trypsin-hydrolyzed bovine casein. Casein is the main protein in cow’s milk. The UK manufacturer lists bovine casein among the ingredients, which matters for cats with a known sensitivity to milk-derived products (see the safety section below).
Dosage: how the product is directed to be given
The Italian manufacturer’s product information lists Zylkene as 75 mg capsules for cats and small dogs. For cats, it gives the following daily amounts by body weight:
| Cat body weight | Daily amount (Italian manufacturer directions) | Total daily dose |
|---|---|---|
| Up to 5 kg | 1 capsule once daily | 75 mg |
| 5 kg to 10 kg | 2 capsules once daily | 150 mg |
These are market-specific directions, not a universal prescription. The package sold in your country may differ, so check the label there before giving the product. Weight bands are the only dosing variable the Italian directions use; they do not adjust for age, health status, or the type of stressor.
#1 Best Overall
- Help Your Pet Cope With External Stress - Zylkene helps your pet cope with changes in their daily routine, such as travel, celebrations, vet visits, home alone, boarding, loud noises, and more
- Alpha-Casozephine - A naturally occurring milk protein found in cow's milk that helps promote calming effects in your pet without drowsiness or other side effects found in other calming chews for dogs
- Lactose-Free and Easy on Sensitive Stomachs - Zylkene's dog calming and cat calming supplements are lactose-free and made with natural ingredients that are easy on sensitive stomachs
- Veterinarian Recommended Daily Calming Support - Zylkene promotes calming in dogs and cats and can be given daily for behavior support and to help deal with unexpected external stresses
- Easy to Administer - Open the capsule of Zylkene and add it to your pet's food daily to help them cope with external stresses like separation and improve daily behavior
For a cat near the top of either band, the arithmetic works out to about 15 mg/kg per day (75 mg at 5 kg, or 150 mg at 10 kg). That figure happens to match the per-kilogram dose of the low-dose group in the 2020 study, but the study ran for six days against a placebo, so the match is arithmetic only and does not show the product works the same way in practice.
Giving the product
- Weigh your cat and confirm which band applies. Cats between bands should be discussed with a veterinarian rather than rounded up or down.
- Check the package directions in your country for capsule opening instructions. The Italian product information describes opening and mixing steps, and those should be followed as written.
- Mix the powder into food or a snack, as the Italian directions allow.
- Ask a veterinarian before changing the dose or continuing the product for a long period.
What the 2020 study tested
The most directly relevant study is Makawey, Iben, and Palme, “Cats at the Vet: The Effect of Alpha-s1 Casozepin,” published in the journal Animals on November 5, 2020. It randomized 60 adult cats into three groups of 20. Cats received either a low dose of alpha-s1 casozepin, a high dose, or a placebo before a veterinary visit. The design was partially double-blind and placebo-controlled.
Rank #2
- Help Your Pet Cope With External Stress - Zylkene helps your pet cope with changes in their daily routine, such as travel, celebrations, vet visits, home alone, boarding, loud noises, and more
- Alpha-Casozephine - A naturally occurring milk protein found in cow's milk that helps promote calming effects in your pet without drowsiness or other side effects found in other calming chews for dogs
- Lactose-Free and Easy on Sensitive Stomachs - Zylkene's dog calming and cat calming supplements are lactose-free and made with natural ingredients that are easy on sensitive stomachs
- Veterinarian Recommended Daily Calming Support - Zylkene promotes calming in dogs and cats and can be given daily for behavior support and to help deal with unexpected external stresses
- Easy to Administer - Open the capsule of Zylkene and add it to your pet's food daily to help them cope with external stresses like separation and improve daily behavior
Study doses are not label advice
The high-dose group received 45 mg/kg daily for three days. The low-dose group received 15 mg/kg daily for six days. These were protocol doses used in the study. They are not a recommendation to exceed the amounts on a current product label.
What the study found
| Outcome measured | Result reported by the authors |
|---|---|
| Absence of sweaty paws, waiting area (high-dose group) | Statistically significant |
| Absence of sweaty paws, examination room (high-dose group) | Statistically significant |
| Reduction in fecal cortisol metabolites | Small and not statistically significant |
The sweaty-paw result was the only significant effect the authors reported. The authors describe their findings as preliminary and call for further research. The study measured one physical sign and one hormone-related measure during a single type of event, a veterinary visit. It does not show that Zylkene reduces anxiety in general, works across different stressors, or treats an anxiety disorder.
Rank #3
- A long-term calming supplement - Zylkene Plus helps promote calm and relaxed behavior when your pet’s routine is altered in situations such as with a new baby, new pet, moving, or left home alone
- Alpha-casozepine and white fish muscle hydrolysate - A naturally occurring protein found in cow's milk is combined with a bioactive marine peptide for a sustained calming effect that’s ideal for stressful periods or recurring situations
- Lactose Free and Easy on Sensitive Stomachs – Zylkene Plus dog and cat calming supplements are lactose free and made with ingredients that are easy on sensitive stomachs
- Veterinary formulated Calming Support - Zylkene Plus promotes calming in dogs and cats over longer periods
- Easy to Administer - Give capsules once daily, whole or opened. Can be given during or after mealtime to help pets cope with external stresses and support normal behavior
Side effects and safety
The retrieved sources did not establish an independent comprehensive rate of adverse events in cats. The manufacturer states that no unexpected situation has been reported with daily use at the recommended amounts. That is the manufacturer’s statement, not an independent safety study, and it is not the same as saying the product has no side effects.
- Milk-protein sensitivity: the product is derived from bovine casein. If your cat has a known or suspected sensitivity to milk-derived ingredients, discuss the product with a veterinarian before starting it.
- Unclear cause of behavior change: the UK manufacturer advises discussing behavior changes with a veterinarian, because they can also signal a medical condition. Do not assume a supplement is the right response until a vet has looked at the cat.
- Dose changes: a veterinarian should confirm the dose, especially for a cat near a weight-band boundary or one that is also receiving other treatment.
When behavior changes need a veterinary assessment
Persistent, severe, or new behavior changes call for a veterinary assessment before a supplement is tried as the main response. The UK manufacturer also recommends veterinary or qualified behaviorist guidance for separation anxiety, which is a condition that a supplement alone is not established to treat.
Rank #4
- Calming Supplement: Proprietary strain BL999 specifically formulated to help maintain calming cat behavior
- Cat Calm: Each 30-count box provides a month's supply of calming care powder packets, with each serving delivering beneficial microorganisms to support your cat's behavioral wellness
- Behavior Support: Shown to improve cats displaying anxious behaviors like pacing while promoting positive activities, such as playing and seeking out social contact
- Stress Support: Helps blunt cortisol production, a key stress marker in cats, while supporting immune system health and providing calm for cats comfort
- Veterinarian Trusted: Cat probiotic brand for calming support, trusted by veterinarians to help cats cope with routine changes and location adjustments safely and effectively
When you see the vet, these questions help make the visit useful:
- Is my cat’s current weight band correct for the product I have?
- Does my cat’s history suggest a sensitivity to milk-derived ingredients?
- Could a medical condition explain this behavior?
- If a behaviorist is needed, who should I contact?
Scope of this review
This article does not rank Zylkene against other calming products. The evidence reviewed here did not compare Zylkene with alternatives, so any product comparison would need a separate evaluation using active ingredient, feline evidence, local dosing directions, ingredient sensitivities, and suitability for the specific stressor, with veterinary input.
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Best Value
- Calming Support Supplement: Vetoquinol Zylkene is a calming supplement for large cats and medium dogs that uses alpha-casozepine from milk protein to support calm behavior during loud noise, celebrations, traveling, and other challenging situations
- Non-Drowsy & Lactose-Free: This behavior support supplement is lactose-free, making it the perfect non-drowsy calming support for dogs and cats with sensitive stomachs
- Easy-to-Give Oral Capsule: For easy use, open this oral supplement and sprinkle onto food; for best results, administer 1–2 days before the expected challenging situations or 5–7 days prior for pets needing additional stress support
- Stress-Free Calming Supplement: Ideal for multi-pet homes, easing tension and supporting pets with new people and environments; for dogs 22–32 lb, give 1 capsule; for dogs 33–63 lb, give 2 capsules; and for cats 22+ lb, give 1 capsule
- Everyday Health for Pets: Made with a commitment to transparency, rigorous review, and dependable standards, every product we create supports happier and healthier moments for your pet
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
