Benadryl is the brand name for the drug Diphenhydramine and comes in 25mg, and 30mg capsules.
Benadryl or Diphenhydramine has many uses. The most obvious use for Benadryl is as an antihistamine. A histamine is an inflammatory which can cause skin redness, pain, heart rate increase, drop in blood pressure, swelling, etc.

Benadryl can help treat things such as vaccination reactions, bee stings, insect bites, snake bites, rodent bites, as well as bad blood transfusion reactions.

Benadryl also has a very strong anti-nauseal side effect which helps treat motion sickness.

Side effects for animals include drowsiness, as well as dry mouth and difficulty to urinate when taken in too high of doses.

When treating skin disease from allergies, antihistamines work well with omega 3 fatty acid supplements and should be taken together for the best results.

It should not be used with tranquilizing medications.

Animals may experience hyperactivity reactions when taking Metoclopramide, also known as Reglan, and can take Diphenhydramine to reverse it.