“Benadryl is a great medication for use in dogs with mild-to-moderate allergies. Seasonal allergies, food allergies, environmental allergies, and allergic reactions to snake and insect bites all respond to Benadryl in most cases.” https://www.akc.org/expert-advice/health/benadryl-for-dogs/
“Some Benadryl products contain decongestants as well, and these can be dangerous for dogs.”
Benadryl - a milligram per pound of body weight.
Do not give Benadryl to dogs with glaucoma, high blood pressure or cardiovascular disease.
“1 mg per pound of body weight, given 2-3 times per day.
https://www.petmd.com/dog/general-health/can-you-give-dog-benadryl
If your dog has any of the following conditions, only use Benadryl after consulting your veterinarian:
Angle closure glaucoma
Severe heart failure
Prostatic hypertrophy
Bladder neck obstruction
Seizure disorders
Hypertension
Allergic lung disease
Pregnancy