Nasal decongestants are used to provide relief to inflamed and irritated sinuses, according to FamilyDoctor.org. The sinuses are large cavities behind the eyes and nose that are delicate and easily aggravated. Nasal congestion is often the result of a cold, the flu, allergies or sinus infections, and can cause discomfort and pain from pressure. Nasal decongestants come in pill or nasal spray form. Consult your doctor before taking any medication.

Pseudoephedrine

Pseudophedrine is a nasal decongestant sold in pill form and is available behind the pharmacist's counter, according to FamilyDoctor.org. Pseudoephedrine is not available for consumers to buy directly off the shelf because of abuse of the drug, but a prescription is not required. Pseudoephedrine works by restricting blood flow to the sinus cavities, according to Drugs.com. This causes the sinus cavity to shrink to its normal size. Common side effects of pseudoephedrine are loss of appetite, a warm sensation, sleeplessness, excitability, dizziness, uneven heart rate, weakness and increased blood pressure. This drug is available in four-hour doses, 12-hour doses and 24-hour doses.

Phenylephrine

Phenylephrine is available over the counter in pill form. Phenylephrine has a similar effect to that of pseudophedrine, restricting blood flow to the sinus cavities to reduce inflammation. Phenylephrine should not be taken by those with heart disease, glaucoma, kidney disease, high blood pressure, sleeping issues, mental illness, circulation issues or a thyroid disorder, according to Drugs.com. Side effects can include dizziness, restlessness, upset stomach, sleep issues, tremors, numbness, lightheadedness and decreased urination. Phenylephrine is available in a single dose taken once every four hours.

Oxymetazoline Nasal Spray

Oxymetazoline is a powerful drug used as the active ingredient in most over the counter decongestant nasal sprays. The drug restricts blood flow to the nasal cavity, reducing nasal congestion. The nose should be blown before use. The medication is sprayed two to three times into each nostril, according to Drugs.com. The nasal spray may cause sneezing. Oxymetazoline is not intended for long-term use and can cause nasal congestion symptoms to worsen if used too much. Drugs.com states that it should only be used for three consecutive days, unless otherwise directed by a doctor.