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Dr Karen Martin
Reviewed by Dr Karen MartinReviewed on 19.10.2023 | 3 minutes read

Phenylephrine is used to temporarily relieve symptoms of congestion caused by colds, flu, and allergies. It works by reducing the blood flow in your nose and reduces swelling and discomfort allowing you to breathe more easily. It is one of the active ingredients in many over-the-counter cold and flu medications, such as Sudafed PE as well as many others. It can come in many different formulations, such as capsules, liquids, and tablets, and can be purchased from a pharmacy or healthcare retailer. Phenylephrine is often combined with other products used to treat colds and flu.

Who is it for?

This medication can be used by patients over the age of 16, however some products with lower doses can be used in children over 6 years old under guidance from a pharmacist. It is used for relieving cold, flu, and allergy symptoms associated with congested blocked noses.

How does it work?

Phenylephrine is what is known as a vasoconstrictor and works by constricting the blood vessels in the nose, this reduces blood flow which in turn reduces swelling. This leads to an improved ability to breathe through your nose and relieves discomfort associated with a blocked nose.

Should anyone avoid taking it?

Phenylephrine is not suitable for children below 6 years, and should be discussed with your pharmacist when anyone under 16 is planning to take it. It should not be used alongside other decongestant medications. If you are pregnant or breastfeeding, you should not use this medication unless directed by your doctor. You should speak to a pharmacist if you have a thyroid disorder, diabetes, heart disease, or high blood pressure.

Are there any side effects?

As with any medications, some people are bound to get some unwanted side effects. Some of the common ones include nausea, headaches, dry mouth, agitation, nervousness, and insomnia. In some rare cases, people can develop fast, uneven, or pounding heartbeats (palpitations). If this happens, you should stop taking the medication and seek medical advice.

Are there any side effects?

In the US, both phenylephrine and pseudoephedrine are commonly used decongestants for relieving nasal congestion associated with conditions like the common cold, hay fever, or sinusitis. However, there are notable differences between the two, particularly regarding their availability, effectiveness, and regulatory status.


Phenylephrine is readily available over the counter in pharmacies and shops without requiring a prescription. On the other hand, pseudoephedrine, while also available without a prescription, is subject to stricter regulations due to its potential involvement in the illicit production of methamphetamine.


In terms of effectiveness, pseudoephedrine is generally regarded as more potent in relieving nasal congestion compared to phenylephrine. While both medications work by constricting blood vessels in the nasal passages, pseudoephedrine is often considered more effective in this regard. However, individual responses to each medication may vary.

Rebound congestion

Both phenylephrine and pseudoephedrine have the potential to cause rebound congestion with prolonged or excessive use.

Rebound congestion, also known as rhinitis medicamentosa, occurs when the blood vessels in the nasal passages become dependent on the decongestant medication for normal function. When the medication wears off, the blood vessels may dilate excessively, leading to a worsening of nasal congestion or a return of symptoms.

While rebound congestion is more commonly associated with prolonged use of nasal decongestant sprays, oral decongestants like phenylephrine and pseudoephedrine can also contribute to this phenomenon if used for an extended period or at higher-than-recommended doses.

Side effects

Both phenylephrine and pseudoephedrine can cause side effects such as increased heart rate, elevated blood pressure, insomnia, nervousness, and dizziness. However, pseudoephedrine may have a higher incidence of side effects due to its stronger stimulant properties.

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This article has been written by UK-based doctors and pharmacists, so some advice may not apply to US users and some suggested treatments may not be available. For more information, please see our T&Cs.
Dr Karen Martin
Reviewed by Dr Karen Martin
Reviewed on 19.10.2023
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