Benadryl is almost certainly safe for your dog if they are at full health. However, there are several contraindications and interactions associated with Benadryl.

The sections below will help you to determine whether your pet is unsuitable for treatment with this medicine. Information listed relates to the two most common active ingredients, diphenhydramine and cetirizine.

Medical Conditions

If your dog suffers with any of the following medical conditions it’s strongly advised that you notify your vet prior to use:


Hyperthyroidism (overactive thyroid), urinary bladder blockage, stenosing peptic ulcer, enlarged prostate, high blood pressure, glaucoma, eye pressure, severe constipation, antihistamine allergy.


Eye pressure, kidney/liver disease, inability to urinate, antihistamine allergy.


Do not mix Benadryl with any of the following substances. Benadryl may be unsuitable for your pet if they have to take any of the following medicines or supplements:


Eliglustat, levomethadyl acetate, potassium chloride, potassium citrate, propoxyphene, sodium oxybate, tamoxifen, thioridazine, topiramate, zonisamide.


No known severe interactions.

I Just Gave Benadryl To An Unsuitable Dog!

If you’ve given Benadryl to a dog who you think could be unsuitable do not panic, but call your vet for advice right away. Once you’ve called the vet and followed their instructions your dog will usually be fine, but monitor them closely for unforeseen or serious side effects over the next 24 hours and be prepared to act quickly.