Phenylephrine: Uses, Side Effects & Safety

What it is and what it's used for

Phenylephrine is a decongestant medicine. It is used to relieve a blocked, stuffy nose caused by the common cold, flu, sinus congestion, and allergic rhinitis (hay fever). When the nose is blocked, breathing through the nose becomes difficult and sleep and eating can be disturbed; a decongestant aims to open the nasal passages so that breathing feels easier.

Phenylephrine is available in two main forms. Oral tablets and syrups work through the whole body and are very often combined with other medicines — such as paracetamol for fever and pain, or an antihistamine for sneezing and a runny nose — in popular cold and flu remedies. Nasal drops and sprays act directly inside the nose and usually give quicker relief of congestion, but they are meant for short-term use only.

In India, phenylephrine is widely available without a prescription in pharmacies, both on its own and in combination products. Well-known combination cold remedies containing phenylephrine include brands such as Sinarest and Crocin Cold & Flu, though brands vary and the exact combination should always be checked on the pack. Even though it is easy to buy, it is not suitable for everyone, especially people with high blood pressure or heart problems, so it should be used with care.

How it works (simple language)

When you catch a cold or have an allergy, the blood vessels inside the nose swell up, and the lining of the nose produces extra mucus. This swelling narrows the nasal passages and causes the blocked feeling. Phenylephrine is thought to work by narrowing these swollen blood vessels in the nose, which reduces the swelling and lets air pass through more freely.

Nasal drops and sprays deliver the medicine straight to the swollen lining of the nose, which is why they often act quickly. Oral tablets, on the other hand, have to travel through the body first, and their effect on nasal congestion is generally milder. That is one reason oral phenylephrine is so often sold combined with other cold medicines rather than on its own.

Dosage forms available in India (general info only)

Phenylephrine is commonly available in India as 10 mg tablets and as syrup, often combined with paracetamol, an antihistamine, or a cough medicine in cold and flu products. It is also available as nasal drops and nasal spray for direct use in the nose. Brands vary, so check the label of any cold remedy you buy — phenylephrine hydrochloride is often listed among its ingredients.

Never decide the dose yourself from this article. Always follow your doctor's prescription or the directions on the pack, and check with your pharmacist if you are unsure — especially for children, where the dose depends on the child's weight and age.

Side effects

Common: Headache, dizziness, nervousness or restlessness, difficulty sleeping, nausea, increased sweating, and a rise in blood pressure. Nasal drops and sprays may also cause burning, stinging, dryness, or sneezing inside the nose.

Serious — seek medical care: Chest pain, a very fast or irregular heartbeat, severe headache, severe dizziness or fainting, difficulty breathing, swelling of the face, lips or tongue, or a severe allergic reaction. With nasal drops or spray used for too long, congestion can come back worse than before (rebound congestion). Seek urgent medical help if any of these occur.

Precautions and warnings

• High blood pressure and heart disease: Phenylephrine can raise blood pressure and speed up the heartbeat. Tell your doctor if you have high blood pressure, heart disease, or an irregular heartbeat before using it, and do not use it if your blood pressure is uncontrolled.
• Nasal drops and spray — short-term use only: Do not use nasal drops or spray for more than 3 days in a row unless your doctor tells you to. Longer use can cause rebound congestion, where the nose becomes blocked again as soon as you stop, and you may feel you need the spray constantly.
• Diabetes, thyroid, glaucoma and prostate problems: Tell your doctor if you have diabetes, an overactive thyroid, glaucoma, or an enlarged prostate, as phenylephrine may worsen these conditions.
• MAOI medicines: Do not take phenylephrine if you are taking, or have recently taken, an MAOI antidepressant medicine, as the combination can cause a dangerous rise in blood pressure. Tell your doctor about all medicines you take.
• Children need extra care: Phenylephrine should only be given to young children on a doctor's advice, and the dose must be measured carefully. Nasal drops for children are different from adult strengths, so never use an adult product for a small child without checking.
• Check combination products: Many cold and flu remedies already contain phenylephrine. Taking two such products together can double the dose and increase side effects, so always check the ingredients on every pack.
• Difficulty sleeping: Phenylephrine can cause restlessness and difficulty sleeping, especially if taken late in the evening. If this happens, talk to your doctor or pharmacist about the timing of your dose.

Interactions (general)

Phenylephrine can interact dangerously with MAOI medicines and may reduce the effect of some blood pressure medicines. It can increase blood pressure when taken with some antidepressants and migraine medicines, and combining it with other stimulants or decongestants can increase side effects such as a fast heartbeat and restlessness. Alcohol does not mix well with many combination cold remedies. Always tell your doctor about ALL medicines you take, including herbal and ayurvedic products, before taking phenylephrine.

Pregnancy and breastfeeding (general guidance)

Phenylephrine should only be used in pregnancy if your doctor advises it, as there is limited evidence about its safety in pregnancy and it can affect blood pressure. It is not known for certain how much passes into breast milk, so talk to your doctor before using it while breastfeeding. Always consult your doctor first if you are pregnant, planning pregnancy, or breastfeeding.

Storage

Store phenylephrine tablets and syrup at room temperature, away from heat and moisture, and out of the reach of children. Keep nasal drop and spray bottles tightly closed, do not share them with others, and do not use the medicine past its expiry date.

When to see a doctor

See a doctor if: your blocked nose does not improve after a few days, your symptoms get worse, you develop a high fever, severe headache, facial pain, or green or bloody nasal discharge, or you need a decongestant repeatedly. Seek emergency care straight away for chest pain, a very fast or irregular heartbeat, severe dizziness or fainting, or difficulty breathing.

FAQs

1. What is phenylephrine used for?

Phenylephrine is a decongestant used to relieve a blocked or stuffy nose caused by colds, flu, sinus congestion, and allergies. It works by narrowing swollen blood vessels inside the nose, which reduces swelling and helps you breathe more easily through your nose.

2. How long can I use phenylephrine nasal drops or spray?

Nasal drops and spray should generally not be used for more than 3 days in a row. Using them for longer can cause rebound congestion, where the nose becomes blocked again as soon as you stop using them. If congestion lasts longer than a few days, see a doctor instead of continuing the spray.

3. Can people with high blood pressure take phenylephrine?

People with high blood pressure or heart disease should be cautious, because phenylephrine can raise blood pressure and speed up the heartbeat. If your blood pressure is uncontrolled, or you have heart disease, talk to your doctor before using it, and never take more than the recommended amount.

4. Is phenylephrine safe for children?

Phenylephrine should only be given to young children on a doctor's advice, and the correct children's strength and dose must be used. Adult tablets, syrups, and nasal products are not automatically suitable for children, so check with your doctor or pharmacist before giving phenylephrine to a child.