Not giving human medications to your pet should be something that is a “given”, but you would be surprised how many times it happens. Our warnings against doing so can be confusing to some people since there are many drugs that are commonly used across species, including in people. But there are some significant differences between humans and animals that people need to be aware of. This is an important discussion not just for people who might be tempted to give their pets human medications, but also in case of accidental ingestion.
Pet and human physiology are very different in many ways. These differences can result in risks of both over- and under-dosing pets. For example, human thyroid supplementation medications normally go as high as around 0.2mg. This dose would only treat a 20 pound dog and we have it available in much higher dosages that could be dangerous to people. Similarly, 50mg of diphenhydramine (Benadryl) is plenty for an adult human but only treats a 50 pound dog. In these and other cases, we give a significantly higher dose to animals and you can’t make analogies based on what a human would take.
On the other side of the coin are medications that can easily over-dose or be toxic for pets. A single dose of acetaminophen (Tylenol) can be fatal to a cat. Naproxen (Aleve) is even more toxic and can cause significant damage to the intestines and liver of dogs. Common anticoagulants used by people with heart disease can cause life-threatening bleeding if swallowed by a cat or small dog. Even something as simple as aspirin can be very dangerous to pets and should never be given without veterinary supervision.
Aspirin also illustrates the often significant differences between dogs and cats. When used appropriately, dogs can take aspirin, though they are more susceptible to the gastrointestinal irritation side effects than humans are. Cats don’t have some of the same enzymes that dogs do and can’t break down certain medications as well, making aspirin potentially dangerous at the same dosages that would be safe for dogs. So just because your vet may have told you that something in your medicine cabinet is safe for your dog, you can’t make the assumption that it is also safe for your cat.
The end point is pretty simple. Always talk to your vet and make them aware of anything you have given your pet. NEVER allow your pet to take or have access to human medications unless your veterinarian has approved doing so.