On the other hand, they are useful for treating the main symptom of a cold, insomnia. Antihistamines are good at reducing the itching and sneezing that are associated with hayfever. They may also help the runny nose if they have drying effects. They do not reduce congestion. Use of these drugs can therefore provide one with a dry, non-itchy but still congested nose.
Side effects Their side effects generally include sedation and drying.
For that reason, one should not drink when taking these agents nor should one operate heavy machinery. Operation of an automobile should be done only with caution. The drying is due to anticholinergic effects. Some have more of this than others. This effect is useful for motion sickness, so many of these drugs are used for that purpose.