Is antihistamine harmful to the body?

No: Antihistamines are a class of medication used since the 1940s. They are used to treat allergic conditions and are very safe. The newer generation antihistamines have even less side effects compared to first generation or old antihistamines.

May cause drowsiness: Many older over-the-counter antihistamines may cause drowsiness. Newer, non-sedating second- and third-generation antihistamines are available over-the-counter or by prescription.