Antihistamines are drugs that treat allergy symptoms. When taken by mouth, they come as pills, chewable tablets, capsules, and liquids.
How Antihistamines Help
Antihistamines treat these allergy symptoms well:
Congestion, runny nose, sneezing, itching, or swelling of the nasal passages that allergic rhinitis (hay fever) can cause
Hives and other skin rashes
Itchy, runny eyes
Treating symptoms can help you or your child to feel better during the day and sleep better at night.
How to Take Antihistamines
Depending on your symptoms, you can take antihistamines:
Every day, to help keep daily symptoms under control. Your health care provider may advise you to start taking them before the allergy season begins.
Only when you have symptoms
Before being exposed to things that often cause your allergy symptoms, such as a pet or certain plants
For many people with allergies, symptoms are the worst around 4 a.m. to 6 a.m. Taking an antihistamine at bedtime may help you or your child feel better in the morning during allergy season.
What Antihistamine Is Right for You?
You can buy many different brands and forms of antihistamines without a prescription.
Some work for only 4 - 6 hours, while others last for 12 - 24 hours.
Some are combined with a decongestant, a drug that dries up your nasal passages.
Ask your health care provider what type of antihistamine and what exact dosage is right for you or your child. Make sure you understand the dosing instructions.
Newer antihistamines cause less sleepiness than the older ones. Some of the newer ones are cetirizine (Zyrtec), desloratadine (Clarinex), fexofenadine (Allegra), and loratadine (Claritin).
Do not drink alcohol when you are taking antihistamines.
Store antihistamines at room temperature, away from heat, direct light, and moisture. Do not freeze them.
Keep all medicines where children cannot reach them.
Side Effects of Antihistamines
Ask your health care provider if antihistamines are safe for you or your child, what side effects to watch for, and how they will affect other medicines you or your child take.
Antihistamines are thought to be safe for adults.
Most are also safe for children older than 2 years.
If you are breastfeeding or pregnant, ask your health care provider if antihistamines are safe for you.
Adults who take antihistamines should know how the medicine affects them before driving or using machinery.
If your child is taking antihistamines, make sure the medicine is not affecting your child's ability to learn.
There may be special precautions if you have:
Enlarged prostate or problems passing urine
Heart disease or high blood pressure
Side effects of antihistamines may include:
Feeling nervous, excited, or irritable
Changes in vision, such as blurry vision
When to Call the Doctor
Call your health care provider if:
Your nose is irritated, you are having nosebleeds, or you have any other new nasal symptoms.
Your allergy symptoms are not getting better.
You are having trouble taking your antihistamines.
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David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.