Side effects of the decongestants often include rapid heart rate and insomnia. These medications can also raise blood pressure of some people. Nonprescription antihistamines are helpful, especially if used only at bedtime because they may cause drowsiness. Often the drowsiness will subside after you have taken the antihistamine for 3 to 5 days. Prescription antihistamines are usually very effective in treating and preventing allergy symptoms.
Some people take antihistamines only on the days they are having symptoms.
Others start the medication at the beginning of their usual allergy season and continue taking it until the season is over. It is safe to take antihistamines and decongestants together if you have no medical reason not to take them together. When antihistamines and decongestants do not sufficiently control your allergy symptoms, prescription nasal sprays may be added to your treatment. Depending on a person's other allergy symptoms, sometimes the nasal spray will be the first and only medication required. Allergy shots will desensitize you to the substances that cause your allergies.