Updated December 18, 2014.

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Benadryl, which is the brand name for the drug diphenhydramine, is classified as a first-generation antihistamine and has been used to treat various allergic diseases for many years. It is available over-the-counter without a prescription, and comes in many generic forms.

Despite newer, safer and more effective antihistamines being available over the past 10 to 20 years in the United States, Benadryl continues to be frequently used for allergic rhinitis, urticaria, itching, anaphylaxis, symptoms of the common cold, and as a sleep aid.

Benadryl Side Effects

While Benadryl is effective for the treatment of various allergic conditions, its side effects limit its usefulness. Side effects such as drowsiness, impairment of mental functioning, dry mouth, inability to urinate, and constipation are common with Benadryl.

Because Benadryl can impair mental and motor functioning, it can affect performance at work or school, and can impair a person’s ability to operate a motor vehicle or other potentially dangerous equipment. In fact, a person can be charged with driving-under-the-influence if they are deemed to be at-fault in a motor vehicle accident while using Benadryl.

In addition, Benadryl is short-acting, which means that it needs to be taken every 4-6 hours for continued antihistamine effects.

Benadryl and Children

Benadryl, and other first-generation antihistamines, should be used with caution in children, and preferably under the direction of a physician. Children may experience similar side effects as adults (see above), or potentially experience paradoxical (opposite than expected) side effects such as excitement, irritability and insomnia.

The potential for overdose is a major concern in young children, as it can lead to seizures and problems with their heart rates.

Benadryl and Pregnancy

Benadryl is a commonly used antihistamine during pregnancy, especially because it has a pregnancy category ‘B’ rating. However, no medication is completely safe during pregnancy and therefore should only be used under the direction of a physician. Large doses or overdoses of Benadryl can result in premature contractions during pregnancy, and caution should be used when giving Benadryl near delivery, as the side effects in the newly born infant can include excitement, irritability and seizures.

Benadryl, as well as other antihistamines, are secreted in the breast milk as only a very small amount of the dose taken by the mother, although that amount may still result in side effects in the infant.

Based on the above side effects, Benadryl should not be considered as a preferred antihistamine for routine use. Second-generation antihistamines, such as cetirizine (Zyrtec) or loratadine (Claritin), have fewer side effects, are more effective, and are safer medications for children and during pregnancy.

Learn more about antihistamines for allergies.

<sub>Sources:

Plaut M, Valentine MD. Clinical Practice: Allergic Rhinitis. N Engl J Med. 2005;353:1934-1944.

Simons FER. Advances in H1-Antihistamines. N Engl J Med. 2004;351(21):2203-2217.

Schweitzer PK, Muehlbach MJ, Walsh JK. Sleepiness and Performance During Three-Day Administration of Cetirizine or Diphenhydramine.J Allergy Clin Immunol. 1994;94:716-24.

DISCLAIMER: The information contained in this site is for educational purposes only, and should not be used as a substitute for personal care by a licensed physician. Please see your physician for diagnosis and treatment of any concerning symptoms or medical condition.</sub>