Phenylephrine: 7 things you should know
Medically reviewed by Carmen Pope, BPharm. Last updated on Aug 31, 2023.
1. How it works
- Phenylephrine is a decongestant that constricts (shrinks) dilated blood vessels within the nose, relieving congestion. Injectable forms may also be used to increase blood pressure.
- 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 class of medicines known as nasal decongestants. It may also be called a vasopressor or a selective alpha-1-adrenergic receptor agonist.
- Tablets, chewable tablets, liquid and nasal preparations of phenylephrine are used to treat nasal and sinus congestion.
- Can also relieve congestion in the eustachian tubes (the tubes that drain fluid from the inner ears).
- Phenylephrine for injection may be used in the treatment of low blood pressure, shock, or supraventricular tachycardia.
- 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.
- There are no contraindications for use listed in the manufacturer's labeling.
- Oral and nasal preparations of phenylephrine are available for purchase over the counter.
- Generic phenylephrine is available.
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:
- Sleep disturbances, restlessness, rash or itching, loss of appetite, feeling of warmth or redness under the skin.
- 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.
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 relieves congestion of the nasal passages and is found in many cold and flu remedies. There is some controversy over whether it works at the dosages usually found in over-the-counter products. Sleeplessness is a common side effect.
- 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.
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
- diabetes medications, such as metformin, glimepiride, glipizide, glyburide, or insulin
- ergot derivatives, such as dihydroergotamine
- heart medications, such as atenolol, betaxolol, bisoprolol, carvedilol
- migraine medications, such as dihydroergotamine
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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- Phenylephrine. Updated 07/2023. Somerset Therapeutics, LLC https://www.drugs.com/pro/phenylephrine-hydrochloride-injection.html
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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