Sometimes clearing these symptoms can actually help get rid of the underlying problem. For example, opening the nasal passages may help the body to cure itself of a bacterial sinus infection by allowing air to circulate properly into the sinuses. Most of the time, though, these medicines don't act to cure but do act to comfort. Both antihistamines and decongestants are drugs, but each is a totally different type of drug. There are many forms of each of these two different drug types.
Antihistamines work in a completely different way.
These medicines reduce the swelling of the nasal lining by reducing the effect of histamines produced by our bodies. Each particular class of antihistamine drug affects individual people differently, and each person responds a little differently to each medicine. Individual reactions are true of every drug to some extent, but there are exceptionally wide personal variations in reactions to antihistamines. The side effects of these drugs are mostly changes in mood or alertness. Some people have obvious drowsiness or irritability, but other people don't seem to be affected in those ways at all.