(Benadryl® is another name for this medication.)
Use: Diphenhydramine is primarily used to treat signs associated with allergic reactions to drugs or to environmental allergens.
Side Effects: The most common side effect, which is desirable in many cases, is sleepiness and sedation. Most animals will become tolerant to this effect with time and the sleepiness will wear off. Dry mouth and inability to urinate are also a possible side effect. Infrequently, diphenhydramine may cause gastrointestinal distress such as vomiting, decreased appetite or diarrhea. Cats may become unusually excited while taking this drug.
Precautions: Working dogs (e.g., guide dogs, search dogs, hunting dogs, sled dogs, and rescue dogs) may become overly sedated and unable to perform their duties while on this drug.
Directions: Dogs and cats usually receive this drug orally up to three times daily as a tablet, capsule or liquid.
Remember: Diphenhydramine should be stored in a tight, light resistant, childproof container away from all children and other household pets. Keep at room temperature; do not allow the liquid to freeze.
If you miss a dose of this medication you should give it as soon as you remember it, but if it is within a few hours of the regularly scheduled dose, wait and give it at the regular time. Do not double a dose as this can be toxic to your pet.