‘Werewolf Syndrome’ Dog Chews: The Exact FSA Products to Check

An old safety notice can remain relevant when the product lasts longer than the headline. Several Barkoo and Chrisco dog chews listed by the Food Standards Agency carry dates in 2027, which means a packet bought online or abroad may still be in a UK cupboard.

The FSA first published its advice in January 2025 and updated it on 14 February 2025. It followed European reports of severe neurological and behavioural signs informally described as “werewolf syndrome”, including panic, aggression, spasms and epileptic-type seizures. Some reported cases were fatal.

The UK position is narrower than the name suggests. The FSA says there is no confirmed distribution of the affected products in the UK, no cases have been detected here and no unsafe dog chews have been identified in the UK. Its advice addresses specific products that owners may have obtained from international sellers—not every chew, every rawhide or every product made in China.

Check the identifiers, not just the photograph

Similar chews can look almost identical once they are out of the bag. Compare the brand, exact product name, pack size, barcode or EAN, product code and date against the live FSA dog-chew notice.

Barkoo products listed by the FSA

Chrisco products listed by the FSA

For the Chrisco products other than item 12457, the date alone is not enough: match it to the exact item, EAN and batch on the original lists. Chrisco’s own withdrawal record provides the batch table.

One discrepancy deserves stating plainly. For item 12624, the FSA page displays a final August 2026 date of 18 August, while Chrisco’s own batch table displays 15 August. Do not use that difference to dismiss an otherwise matching packet. Stop feeding it and ask the seller or manufacturer to confirm the product.

What to do if a packet matches

Do not feed any more of the listed chew. Keep the packet, photograph every side and record where and when it was bought. If it came from an overseas website, preserve the order confirmation and seller details.

Chrisco’s withdrawal notice asks customers to return its listed products to the shop where they were bought for a refund. For a Barkoo or cross-border purchase, follow the seller’s current instructions after keeping the identifying evidence.

Do not donate a matching chew or give it to another animal. Avoid turning a product check into a test feeding: an uneaten packet is not evidence that it is safe, and one previously eaten without visible illness does not clear the remaining chews.

When to contact a vet

The FSA tells owners to seek veterinary advice if a dog is unwell after eating a listed product and to give the vet detailed information about foods and treats the dog has received.

European reports described sudden behavioural changes such as howling, crying and aggression, as well as panic, spasms and epileptic-type seizures. These signs are serious but not unique to this product alert. A dog can show them for other urgent neurological or medical reasons.

If a dog has eaten a matching chew and develops a sudden behavioural change, loss of coordination, spasm, seizure or collapse, contact a vet immediately. Take the packet or clear photographs. Do not attempt to diagnose “werewolf syndrome” at home, and do not wait for the whole reported pattern to appear.

Vets who suspect a case connected with these products can report it to the FSA at the route given in the official notice, using incident reference I-009-004.

What later investigations added

The informal label should not be mistaken for a settled diagnosis or cause. In March 2025, the Dutch Food and Consumer Product Safety Authority said its testing of Barkoo chews had not found contamination capable of explaining the neurological signs. Because of the number of reports in several countries, it kept its precautionary warning in force.

In July 2025, retailer Zooplus published the result of its own commissioned investigation. It said independent toxicologists considered methionine sulfoximine, or MSO, the most plausible explanation. The company said MSO can form when raw bovine hide is treated with unauthorised bleaching agents.

That is a company-reported hypothesis, not a final regulatory finding. Zooplus also said MSO had not been detected in affected dogs and that no conclusive research established its effects or a harmful threshold in dogs. The company withdrew potentially affected chews, ended its relationship with the manufacturer and said it would phase rawhide products out of its range.

Taken together, these records explain why the safest statement is still cautious: reports prompted specific withdrawals and continuing avoidance advice, but the causal mechanism has not been conclusively demonstrated in dogs.

What this alert does not say

It does not establish that every dog chew imported from China is unsafe. It does not identify a UK outbreak. It does not show a human-health risk; the FSA says there is no evidence of one from the listed products.

It also does not give a visual test for contamination. Colour, smell and texture cannot replace the package identifiers. A matching name without the right code may be a different product; a matching code deserves action even if the chew looks ordinary.

The proportionate response is a precise cupboard check, not a general panic. Match the full details, stop a listed product, preserve the evidence and use a vet—not social-media symptom comparisons—if the dog may be affected.

Sources and update record

• Food Standards Agency: products and precautionary advice
• Chrisco: six-product withdrawal and batch table
• Dutch regulator NVWA: investigation result and continuing warning
• Zooplus: July 2025 investigation update

Last checked: 23 August 2026, 14:20 BST. The FSA page was last updated on 14 February 2025. This revision adds later regulator and retailer investigation records while preserving their different evidence limits.