Decongestants are chemically related to adrenalin, the natural decongestant, which is also a type of stimulant. Therefore, the side effects of systemic decongestants include:

• a jittery or nervous feeling
• difficulty in going to sleep
• elevation of blood pressure and pulse rate
• difficulty with urination

Decongestants should not be used by patients who have an irregular heart rhythm (pulse), high blood pressure, heart disease, or glaucoma. Furthermore, decongestants are often used as ingredients in diet pills. So, to avoid excessively stimulating effects, patients taking diet pills should not take decongestants.

Because they are directly applied, topical decongestants create a stronger stimulation than decongestants taken by mouth. If topical decongestants are used too frequently, patients risk developing “rebound congestion”. Because the decongestant impairs the circulation in the nose, after a few hours it stimulates the vessels to expand to improve the blood flow again, which creates renewed congestion. In infants, this rebound effect can develop in two days, whereas in adults, it often takes several more days to become established. This side effect makes many patients dependent on chronic usage just to breathe normally.

An infant taken off topical decongestants for 12 to 24 hours is cured, but well-established cases in adults often require more than a simple “cold turkey” withdrawal. They need decongestants by mouth, sometimes corticosteroids, and possibly, for patients who continuously have used the sprays for months and years, a surgical procedure to the inside of the nose. For this reason, the labels on these types of nose sprays contain the warning “Do not use this product for more than three days.”