(HealthDay News) -- Antihistamines are medications used to prevent or treat allergy symptoms. Many of these medicines may be bought without a doctor's prescription.

The American Academy of Family Physicians has issued these guidelines for people who take an over-the-counter antihistamine:

• Before you take an antihistamine, talk to your doctor if you have a chronic health condition, including heart disease, high blood pressure or thyroid disease.
• Before you take an antihistamine, talk to your doctor if you also take a sleeping pill, sedative or muscle relaxant. These other medicines may interact with an antihistamine.
• If you take an antihistamine that is combined with a decongestant or pain reliever, carefully check the label for potential interactions with your other medications.
• Be careful that you aren't taking more than one medication that contains an antihistamine. This could cause you to take more than you need.