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:
- Congestion, runny nose, sneezing, or itching
- Swelling of the nasal passages
- 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
- 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 to 6 hours, while others last for 12 to 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 how much to use and how many times a day to use it. Be sure to read the label carefully. Or ask your pharmacist if you have questions.
- Some antihistamines cause less sleepiness than others. These include 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 antihistamines.
- 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 antihistamines may affect other medicines you or your child take.
- Antihistamines are thought to be safe for adults.
- Most antihistamines are also safe for children over 2 years old.
- 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 for using antihistamines if you have:
- Enlarged prostate or problems passing urine
- Overactive thyroid
- Heart disease or high blood pressure
Side effects of antihistamines may include:
- Dry mouth
- Feeling nervous, excited, or irritable
- Changes in vision, such as blurry vision
- Decreased appetite
When to call the doctor
Call your doctor 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
Corren J, Baroody FM, Pawankar R. Allergic and nonallergic rhinitis. In: Adkinson NF Jr., Bochner BS, Burks AW, et al., eds. Middleton's Allergy Principles and Practice. 8th ed. Philadelphia, PA: Elsevier Mosby; 2013: chap 42.
Wasserman SI. Approach to the person with allergic or immunologic disease. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders Elsevier; 2011:chap 257.
Update Date 5/18/2014
Updated by: Stuart I. Henochowicz, MD, FACP, Associate Clinical Professor of Medicine, Division of Allergy, Immunology, and Rheumatology, Georgetown University Medical School. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.