Benadryl (diphenhydramine) usually begins to take effect in dogs within about 30 minutes, though it can range up to an hour. It is absorbed quickly, and owners can generally expect to see signs of relief from allergic reactions, itching, or anxiety within this timeframe.
The medication is typically dosed at about 1 mg per pound of body weight, given two to three times a day, but dosage and frequency should be confirmed with a veterinarian. Effects such as drowsiness are common and expected, and the sedative effect may vary depending on the dose and individual dog.
In summary, most dogs will show Benadryl's effects within 30 to 60 minutes after administration.
