You’re worried your dog is sick, so you take him to your veterinarian. After a thorough checkup, the doctor tells you that Viagra may be the answer to your dog's problems. The answer to your neutered male dogs problems.

No, it’s not your vet’s idea of a joke. It’s actually perfectly legitimate to prescribe Viagra for a dog, even if he’s neutered — but not for the reasons you might think.

Different Species, Different Uses (Sometimes)

Viagra, or sildenafil citrate, is best known for fixing erectile dysfunction in human males, but because it works by improving blood flow, it can also be effective in treating pulmonary hypertension, a disorder that causes high blood pressure in the arteries of the lungs. You should never give your pet a human medication unless directed to do so by your veterinarian, but for dogs with certain pulmonary problems, Viagra may be the key to improving the condition. And it’s not the only human medication veterinarians can — and do — prescribe.

Another surprising remedy is Botox, used to treat certain eye problems in dogs.

The practice of prescribing a drug for a condition (or species) other than what it was originally developed for is called off-label use. It allows veterinarians to treat medical conditions that are not priorities for big drug companies. The majority of drugs used in veterinary medicine come from human medicine, especially drugs for more specialized treatments, such as cancer.

Vets Need To Be Pharmacists, Too

Veterinarians need to know more about pharmacology than their physician counterparts. In human medicine, all drugs are approved by the Food and Drug Administration, meaning that they have undergone significant scrutiny for safety and efficacy. But just because a drug is safe for humans, doesn’t mean it’s safe for animals, Therefore, vets must often use fairly limited evidence to treat other species with differences in drug metabolism and action.

When a veterinarian believes that a human medication can help an animal, she’ll prescribe it. This has been the case for decades, of course, but the practice has been legal only since 1994, when Congress passed the Animal Medicinal Drug Use Clarification Act regulating the conditions under which such use is acceptable.

Even before the legislation was in place, however, there was a working system for prescribing human drugs to pets. Veterinarians relied on peer-reviewed studies, clinical trials, and published formularies that included suggestions for safe uses and dosages of human medications given to companion animals.

More Choices Available

Today, with the legal issues mostly cleared up, veterinarians and their patients have more options and better access to medications — and more medications are available specifically for pets. Vets have always been glad to provide in-house pharmaceutical services, and, in general, pharmacists have been willing to fill prescriptions written by vets. But recently, online retailers, big-box stores, and specialty pharmacists have recognized pets as an expansion market. These developments open the door to even more progress, including discussions on generic meds and price shopping.

Chances are you won’t be walking out with a prescription for Viagra or Botox the next time you go to the veterinarian’s office, but you should talk with the doctor about your pet’s treatment options. Knowing how and why certain drugs are prescribed can help pet owners understand health care options — including some that save money. A good vet will discuss medications, tell you what side effects to look for, and encourage you to call with questions or concerns.

This article was written by a Veterinarian.