Diphenhydramine (Benadryl®, Sominex®, and many others) is an antihistamine medication available both over the counter and with a prescription. There are many different forms of diphenhydramine (oral, topical, and injectable forms), and the drug is used for a variety of different purposes.
Diphenhydramine oral products are available in the following forms and strengths:
- Diphenhydramine 25 mg capsules, tablets, Liqui-Gels®, or quick-dissolving strips
- Diphenhydramine 50 mg capsules or tablets
- Diphenhydramine 12.5 mg per 5 mL liquid (12.5 mg per teaspoonful)
- Diphenhydramine 12.5 mg pre-filled single use spoons.
The medication works by blocking H1 receptors. Since allergic reactions are partly caused by the release of histamine from certain cells in the body, the drug can help relieve or prevent allergy symptoms. Diphenhydramine also blocks acetylcholine receptors, an action which produces some of the bothersome side effects of the medication (such as dry mouth or difficulty urinating) but also makes the drug useful for some uses (such as for Parkinson's disease or for relieving a runny nose due to the common cold).
(Click Diphenhydramine for a list of other available diphenhydramine products, to find out when and how to take this medicine, and for general warnings and precautions for this product.)