Allergies Common Treatments Print Before You Buy Benadryl Facts About the Popular Cold and Allergy Remedy By Kristina Duda, RN Updated June 30, 2019 Jupiterimages/Photolibrary/Getty Images More in Allergies Common Treatments Nose & Eye Allergies Drug & Latex Allergies Contact Dermatitis Food Allergies Skin Allergies Animal & Insect Allergies Urticaria & Angioedema Benadryl is a popular antihistamine drug that can be purchased over the counter without a prescription. It is effective in treating symptoms of the cold and mild allergy, including a runny nose, sneezing, hives, and itching. It is available in different generic formulations. Benadryl works by blocking the effects of histamine, a substance released by the body involved in allergies. The drug usually starts to work within an hour. Formulations Benadryl comes in a tablet, liquigel, syrup, chewable tablet, and topical cream formulation. The active ingredient is diphenhydramine, the amount of which can vary by formulation: Tablet - 25 to 50 milligrams (mg)Liquigel - 25 mgAdult syrup - 12.5 mg per five milliliters (mL)Children's syrup - 6.5 mg per 5.0mLChildren's chewable tablet - 12.5 mgTopical cream - 2 percent per gram Dosages Benadryl is short-acting, meaning that it needs to be taken every four to six hours to ensure persistent relief. It is generally prescribed as follows: For adults and children over 12, the standard dose is 25 mg to 50 mg taken every four to six hours, not to exceed six doses in 24 hours.For children six to 12, a dose of 12.5 mg (one chewable tablet) to 25 mg (one adult tablet) may be taken every four to six hours, not to exceed six doses in 24 hours.For children under six, Benadryl should not be given unless directed to do so by a pediatrician. The topical cream can be used safely in adults and children over six, applied thinly over areas of rash but for no longer than seven days. Side Effects of Benadryl While Benadryl is effective in treating symptoms of the cold and allergy, there may be side effects. Most are mild and usually resolve within a few hours. The most common (occurring in more than one percent of users) are: DrowsinessDizzinessImpairment of mental or motor functionExcitability, primarily in childrenDry mouthConstipationThickening of mucus Benadryl can impair your ability to function and should never be used if you are planning to drive. Many state laws will charge you with a DUI (driving under the influence) if you are deemed to have been impaired by Benadryl. You should never drink alcohol when taking Benadryl as this can only enhance the effect. The same applies to any tranquilizers or sedatives. Contraindications and Considerations You should not use any topical cream containing diphenhydramine if you have chickenpox, measles, broken skin, or large areas of skin that need to be treated. If you experience blurred vision, confusion, painful urination, or have difficulty urinating after taking Benadryl, call your doctor immediately. Moreover, you should stop treatment and seek emergency care in the unlikely event you experience a potentially deadly, all-body reaction known as anaphylaxis (characterized by severe hives, difficulty breathing, abnormal heartbeat, and the swelling of the face, mouth, tongue, or throat). Was this page helpful? Thanks for your feedback! Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life. Sign Up You're in! Thank you, {{form.email}}, for signing up. There was an error. Please try again. What are your concerns? Other Inaccurate Hard to Understand Submit Article Sources Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial policy to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. U.S. National Library of Medicine. "Diphenhydramine." MedLine Plus. Bethesda, Maryland; updated October 24, 2017. Continue Reading