Pet owners worry about drug safety

Authorities and pet owners are beginning to raise serious questions about the safety and effectiveness of animal medicines, mirroring worries over human drugs like the painkiller Vioxx.

Tested on just a couple hundred animals, a drug meant for pets is less apt than a human one to show all its failings until it reaches the market, veterinarians say. More than 700 drugs have been approved for pets, but many others are used legally without explicit approval for animals.

Most pet drugs were first developed for people. But each species of animal — even varying breeds — may react differently to the same drug.

Further, animals can't say if a drug makes them feel bad.

"I can't tell until you see something physical," said Laurryn Simpson of Commerce Township, Mich., who founded the Web site dogsadversereactions.com