Decongestants for Treating Allergies

A decongestant nasal spray can provide fast allergy relief.
A decongestant nasal spray can provide fast allergy relief.

When you have an allergic reaction, your body traps allergens by bringing more blood to the lining of the nose. Inflammation and swelling occur. This causes more mucus production. The combination of inflammation, swelling, and mucus causes nasal congestion and limits air flow.

Decongestants relieve stuffy noses and make it easier for you to breathe by narrowing blood vessels and reducing blood flow to mucous membranes. This results in less mucus and congestion. Decongestants also help open the nasal cavity and sinuses, often within minutes.They are a relatively safe medication when used to treat nasal allergies, and they work even if you take them after you've been exposed to an allergen.


Decongestants are available both over the counter and by prescription, and there are many different types and combinations. You can even get allergy medications that are a combination of decongestants and antihistamines. If the decongestant you use doesn't work, talk to your pharmacist or doctor. There are many varieties from which to choose.

Decongestants are available as tablets, nasal sprays or drops. Nasal sprays or drops deliver medicine directly into your nose. They can provide almost instant temporary relief of the nasal congestion that develops from allergic reactions.  However, continued use can cause a stuffy nose that doesn't clear and irritate the inside of the nose.  Be careful not to overuse.

Oral decongestants take more time to reduce congestion because they have to be swallowed and absorbed by the body. They start working after about an hour or two. Decongestant tablets are the best form to use if you need allergy symptom relief for more than a few days. Tablets should not be taken by people with heart problems, diabetes, enlarged prostate, high blood pressure, or by nursing mothers or those taking beta-blockers (blood pressure and heart medication). There can also be problems with restlessness, nervousness, insomnia.

See the next page to see more common side effects of decongestants and how to use them safely.


Using Decongestants Safely

To get the best results from decongestants and use them safely in the treatment of allergies

  • Don't take them if you have heart problems, high blood pressure, diabetes, enlarged prostate, or an overactive thyroid.
  • Use nasal sprays or drops when you need instant congestion relief.
  • Don't use decongestant nasal sprays or drops for more than 3 or 4 days.
  • Use oral decongestants when you need symptom relief for more than a few days.
  • Avoid taking decongestants before bed.
  • Avoid other stimulants such as caffeinated coffee, teas, colas, diet pills, or "pep" pills while you're taking decongestants.
  • If you're taking beta-blockers, a blood pressure medication, talk with your doctor before using decongestants.
  • Talk with your doctor before taking any medications if you're pregnant, nursing, or plan to become pregnant.

If you're bothered by side effects, your doctor can often help by changing:


  • How much medication you take. Sometimes side effects can be stopped or minimized by reducing the dose. Or, your doctor may lower the dose and then raise it more slowly.
  • When you take the medication. You may be able to cope with drowsiness or insomnia, for instance, by taking your medication in the evening or first thing in the morning.
  • How you take the medication. Taking your medication in smaller doses several times a day rather than in one dose can help. Taking your medicine with food might eliminate side effects such as nausea.
  • The type of allergy medication. A different allergy medication may be able to stop your symptoms with fewer or less severe side effects.

Always talk with your doctor before changing how you take your medication.

Common Side Effects of Decongestants

Decongestants can cause sleep problems and nervousness due to overstimulation of the brain. They can also cause other side effects, such as raising blood pressure. This feeling of nervousness often wears off after a couple of weeks, but for people with heart problems and high blood pressure, decongestants can be dangerous.

Serious Side Effects of Decongestants

One of the most dangerous side effects is that they can make existing heart problems worse. So always let your doctor know if you have high blood pressure or heart disease. And, if you've been diagnosed with either of these two medical problems, don't take decongestants for allergies without first discussing it with your doctor.

Decongestants can also produce a number of less severe side effects, including:

  • restlessness
  • nervousness
  • sleeplessness
  • loss of appetite
  • rebound effect (from nasal sprays or drops)
  • increased blood pressure
  • nausea
  • urinary problems
  • visual difficulties
  • irritation of the nasal lining (from sprays or drops)
  • headache
  • faster heartbeat

Watch Out for Nasal Rebound

One of the big disadvantages of nasal spray decongestants is that overusing them can actually cause the blood vessels in the nose to swell, making your stuffy nose even worse. This is called the rebound effect. The medical term for this type of nasal reaction is chemical rhinitis or rhinitis medicamentosa.

The rebound effect can last for days. If your stuffy nose is getting worse, you may be suffering from a rebound effect, so stop taking the medicine and call your doctor.

Decongestants Can Interact With Other Medications

Before taking any new medication, let your doctor know what other drugs and supplements — both prescription and over-the-counter medications — you take.

The following medications can make decongestant side effects worse:

  • antibiotics and antifungal medications
  • antidepressants such as monoamine oxidase inhibitors (MAOIs such as Parnate and Nardil) and tricyclic antidepressants or TCAs, in general
  • blood pressure or heart medications, such as beta-blockers, guanethidine, methyldopa, and rauwolfia
  • nonsteroidal anti-inflammatory drugs such as indomethacin for arthritis

Nasal decongestants can alter the effects of the following types of medications:

  • anti-Parkinson agents, such as bromocriptine mesylate
  • blood pressure or heart medications, such as beta-blockers
  • caffeine products such as coffee, tea, or colas
  • insulin or oral hypoglycemic agents, used for elevated blood glucose and diabetes
  • antipsychotic drugs in general
  • theophylline taken for respiratory problems
  • urinary acidifiers or alkalinizers taken for bladder problems

For more information about allergies and allergy treatments, see the next page.


Lots More Information

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Written by Karen Serrano, MD Emergency Medicine resident at the University of Wisconsin-Madison.

Reviewed by Lisa V. Suffian, MD

Instructor of Clinical Pediatrics in the Division of Allergy and Pulmonary Medicine at Saint Louis Children's Hospital, Washington University School of Medicine

Assistant Clinical Professor in the Department of Pediatrics at Cardinal Glennon Children's Hospital, Saint Louis University

Board certified in Allergy and Immunology

Last updated June 2008