A dog given Ibuprofen by its owners for a neurological condition became so distressed it chewed off its own paw.
Tony O'Neil, 55 and Donna Lynch, 44, of Great Yarmouth, Norfolk, gave the painkiller to brindle mastiff Jessie, when her prescribed medication ran out.
The RSPCA said the drug would not have helped the pain of the chewed paw and could be toxic to dogs.
They were found guilty of charges under the Animal Welfare Act 2006 and fined by Great Yarmouth magistrates.
Jessie had been suffering from a lame leg caused by her neurological condition, the RSPCA said.
O'Neil and Lynch had previously been given medication but failed to return to the vet when it ran out.
In June 2013, when they eventually took her to a vet, a bandage was unwrapped on her left hind leg to reveal she had completely chewed her own paw off.