It is tempting to reach in the medicine cabinet when our pets are not feeling well, but this can ultimately result in more harm than good. Many over the counter medications that are safe for use in people are toxic to dogs and cats. Even those medications that are safe for use in dogs and cats are not safe at the same dosages as those used in people.
Tylenol for instance is extremely toxic to cats and dogs and can lead to kidney failure as well as severe bleeding ulcers. It should never be used. Neither should Aleve as it can cause similar problems. Even milder forms of pain relievers such as aspirin can cause these signs at the human dosages listed on the bottles. In addition, aspirin can be extremely dangerous if given with other forms of medications such as steroids and anti-inflammatories dispensed from your veterinarian.
Antihistamines dispensed over the counter often have additional drugs in them for decongestion or to prevent drowsiness in people. These extra ingredients can cause dangerous heart arrhythmias in pets. Even something as mild as vitamin supplements often contains concentrations of certain ingredients that can be harmful to pets. For these reasons it is always advisable to consult your veterinarian before administering ANY over the counter medication to your pet.