Phenylephrine Patient Tips

Medically reviewed by Carmen Pope, BPharm. Last updated on Aug 12, 2025.

1. How it works

• Phenylephrine is used to temporarily relieve nasal congestion (oral/nasal forms) caused by colds, allergies, or hay fever. Injectable phenylephrine may be used in a hospital setting to increase blood pressure in adults.
• Phenylephrine works by directly stimulating alpha-1 adrenergic receptors in the arteries causing vasoconstriction (narrowing of the blood vessels). This reduces nasal congestion by preventing fluid from draining from the blood vessels into the tissues lining the nasal passages. Phenylephrine may also cause dose-dependent increases in blood pressure and reductions in heart rate and cardiac output (particularly in people with preexisting cardiac dysfunction) by increasing systemic vascular resistance.
• Phenylephrine belongs to the drug class called decongestants. It may also be called a vasopressor or a selective alpha-1-adrenergic receptor agonist.

2. Upsides

• Used to temporarily unblock a nose or relieve sinus pressure in people with nasal and sinus congestion caused by colds, allergies, or hay fever (tablets, chewable tablets, liquid and nasal phenylephrine preparations). Can also relieve congestion in the eustachian tubes (the tubes that drain fluid from the inner ears).
• Injectable phenylephrine may be used in a hospital setting to increase blood pressure in adults with significantly low blood pressure caused primarily by vasodilation (a widening of the blood vessels), as a result of septic shock or anesthesia.
• May be used off-label for ischemic priapism that persists following aspiration or irrigation or for low blood pressure in people with obstructive hypertrophic cardiomyopathy.
• No contraindications listed in manufacturer's labeling. Available over 60 years, predating current rigorous FDA scrutiny for newer medicines.
• Oral and nasal preparations of phenylephrine are available for purchase over the counter.
• Generic phenylephrine is available.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

• Flushing (warmth, redness, or tingly feeling), loss of appetite, and feeling restless or excited (especially in children) are the most common side effects reported. Sleep disturbances, rash or itching may also occur.
• May not be suitable for some people including those with angina, high blood pressure, heart disease, diabetes, a thyroid disorder, spinal cord injuries, septic shock, or with circulation disorders such as peripheral vascular disease. It may also slow the heart rate or decrease how much blood the heart pumps out into the lungs. Should not be used by women who are pregnant or breastfeeding unless under a doctor's advice.
• May interact with some other medications including monoamine oxidase inhibitors and oxytocic drugs.
• Not suitable for children under four. Always talk with a doctor before giving cough or cold medicines to children.
• The injectable form of phenylephrine contains sodium metabisulfite, a sulfite that may cause allergic reactions in susceptible people. The injection may also cause sloughing of tissue if leakage occurs around the injection site.
• Not recommended for routine use following septic shock.
• In 2023, an FDA advisory panel concluded that oral phenylephrine was ineffective as a decongestant, and no better than a placebo. Poor bioavailability (only 3% unchanged) and a lack of rigorous clinical trials contribute to ineffectiveness. The nasal spray form of phenylephrine is still considered effective.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

Phenylephrine is used to temporarily unblock a nose or relieve sinus pressure in people with nasal and sinus congestion caused by colds, allergies, or hay fever. Injectable phenylephrine may be used in a hospital setting to increase blood pressure in adults with significantly low blood pressure caused primarily by vasodilation. Flushing, loss of appetite, and feeling restless or excited (especially in children) are the most common side effects reported. In 2023, an FDA advisory panel concluded that oral phenylephrine was ineffective as a decongestant, but the nasal spray form of phenylephrine is still considered effective.

5. Tips

• Use as directed for short periods only. Phenylephrine only provides symptom relief, it does not cure a cold.
• Take with a full glass of water.
• Chewit the chewable tablet before swallowing. Shake the oral suspension well before measuring out the correct dose. Always use a proper measuring spoon or dropper to ensure you are getting the correct dose.
• Do not give phenylephrine to children without talking to a doctor first. Phenylephrine must never be given to children under the age of four.
• Call your doctor if your symptoms have not improved within seven days of treatment, or if you develop a fast, pounding, or uneven heartbeat, severe dizziness or anxiety, severe headache, fever, or rash.
• Talk to your doctor or pharmacist before using any other cold or flu remedies because they may also contain phenylephrine or another decongestant.
• Do not use phenylephrine if you are pregnant or breastfeeding unless under a doctor's advice.

6. Response and effectiveness

• The decongestant effect of phenylephrine in cold or flu remedies should be noticeable within 15 to 30 minutes, and the effects last less than 4 hours. A rapid increase in blood pressure is usually seen following an intravenous dose that persists for up to 20 minutes. After an IM dose, it may take 10 to 15 minutes for a blood pressure increase to be seen which will last 1 to 2 hours.
• There is some controversy over the effectiveness of phenylephrine at dosages found in over-the-counter cold and flu remedies.

7. Interactions

Medicines that interact with phenylephrine may either decrease its effect, affect how long it works, increase side effects, or have less of an effect when taken with phenylephrine. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with phenylephrine include:

• alpha-blockers, such as alfuzosin, doxazosin, prazosin, or terazosin
• antidepressants, such as amitriptyline, amoxapine, clomipramine, doxepin, imipramine, isocarboxazid, or phenelzine
• atomoxetine
• atropine
• benztropine
• cannabinoid
• clozapine
• diabetes medications, such as metformin, glimepiride, glipizide, glyburide, or insulin
• digoxin
• duloxetine
• ergot derivatives, such as dihydroergotamine
• fentanyl
• heart medications, such as atenolol, betaxolol, bisoprolol, carvedilol
• levodopa
• methylphenidate
• migraine medications, such as dihydroergotamine
• oxybutynin
• orphenadrine
• selegiline
• venlafaxine.

Note that this list is not all-inclusive and includes only common medications that may interact with phenylephrine. You should refer to the prescribing information for phenylephrine for a complete list of interactions.

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Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use phenylephrine only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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