Acetaminophen is extremely toxic to cats. It has limited uses in dogs.
Although the drug is generally considered safe for people, several side effects are widely known. Liver damage is a well-publicized side effect from acetaminophen ingestion.
The October 10, 2008 issue of The Week contained a blurb that described a new discovery. Here is an excerpt.
A five-year study of 200,000 babies and children has shown that if an infant is given acetaminophen, her or she is 46 percent more likely to have developed asthma by 6 or 7.
Acetaminophen is a human medicine. The study involved children, not pets. What does this have to do with a vet blog?
In practice, I sometimes am pressured by clients to prescribe medications for syndromes that will spontaneously resolve. These clients want to feel like they are doing something to make their pets better.
I admire their desire to help their pets. However, I am very reluctant to prescribe a drug unless I have a strong reason to believe that the medicine will make a positive difference.
Acetaminophen has been on the market for 53 years, and possible side effects are still being discovered. That is a solid reason not to overmedicate my patients.