Decongestants open up the nasal passages and allow the user to "breathe easier." Side effects include nervousness, dizziness and insomnia. Decongestants must be administered cautiously to patients with uncontrolled hypertension as they may experience a change in blood pressure. These drugs may also cause problems with patients who have arrhythmias and hyperthyroidism who do not need additional cardiac stimulation.

Nasal sprays reduce blood flow to the nasal area. The constriction promotes shrinkage of the mucous membranes thereby relieving the feeling of stuffiness. Nasal decongestants sprays such as Neo-synephrine should be restricted to 3-4 days of therapy because they can cause rebound congestion. Patients who increase the frequency of application can become toxic and perpetuate rebound congestion. Rebound congestion can be prevented by initially using plain saline spray (e.g. Ocean Nasal Spray) to open the nasal passages. Ocean spray should be recommended first and if this is ineffective, only then should a decongestant be administered.

Oral decongestants such as pseudoephedrine (Sudafed™) and phenylpropanolamine (Contact™) have a longer duration of action in comparison to nasal spray decongestants. Oral agents do not have rebound congestion and lack local irritation to the nasal mucosa. These should not be given in anyone who has uncontrolled hypertension. Phenylpropanolamine is also used as a diet pill because of its stimulant effects. It is known as Dexatrim and is available over-the-counter. It should be avoided in the elderly because it may cause central nervous stimulation such as restlessness, agitation, confusion and hallucinations.