The animal was destined for residential premises in West Yorkshire and had been shipped from Australia.
The parcel contained 50 x Gabapentin Apotex 400mg capsules. A statement by the Veterinary Medicines Directorate said: "This product was intended for use in a dog and is not an authorised veterinary medicine in the UK and had not been prescribed by a UK vet for use in the animal. "The medicine was seized under Regulation 25 (Importation of unauthorised veterinary medicinal products) of the Veterinary Medicines Regulations 2013."