Histamine is one of the chemicals released when antibodies overreact to allergens. It is the cause of many symptoms of allergic rhinitis. Antihistamines can help relieve:
- Itching, sneezing, and runny nose (unless combined with a decongestant, antihistamines do not work well for relieving nasal congestion).
- Other allergy symptoms unrelated to rhinitis, including hives and some rashes
If possible, patients should take antihistamines before an anticipated allergy attack.
Many antihistamines are available. They include short-acting and long-acting forms, and come in oral pill and nasal spray forms.
Antihistamines are generally categorized as first- and second-generation. First-generation antihistamines, which include diphenhydramine (Benadryl, generic) and clemastine (Tavist, generic) cause more severe side effects (such as drowsiness) than most newer second-generation antihistamines. For this reason, second-generation antihistamines are generally preferred and recommended over first-generation antihistamines.
There are some notes of caution when taking any antihistamine:
- Antihistamines may thicken mucus secretions and can worsen bacterial rhinitis or sinusitis.
- Antihistamines can lose their effectiveness over time, and a different one may need to be tried.
Review Date: 05/03/2011
Reviewed By: Harvey Simon, MD, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.