Benadryl is an antihistamine. Its active ingredient is diphenhydramine. Diphenhydramine can be given to dogs for a variety of reasons. It can be used for allergic respiratory disease, cough, pruritis (itchy skin) due to allergy, motion sickness, and mild sedation. It should not be used if your dog has urinary retention, glaucoma or hypertyroidism. Side effects include drowsiness and CNS depression (Impaired thinking and perception, decreased heart rate, slow breathing)

The general dose of Benadryl (diphenhydramine) is 2 to 4 mg/kg up to three times day. If your dog weighs 25 lbs (11.3 kg) the dose of Benadryl would be 22.6mg to 45.2mg up to three times a day.

Benadryl tablets are available in 25mg and 50mg strength. If you were using the Benadryl 25mg tablet you could give 1 to 2 tablets up to three times day.

It is worth noting a vet should be consulted to reassure you that your dogs symptoms are not indicative of something more serious.