Phenylephrine

Introduction

Written by Lee Holland, PharmD, MPH
Medically reviewed by Alex Brewer, PharmD, MBA
Updated on November 22, 2023

Phenylephrine (fen il EF rin) is a generic medication prescribed for low blood pressure and pupil dilation. Phenylephrine belongs to a group of drugs called alpha-1 adrenergic receptor agonists.

The approved uses differ based on the form of phenylephrine your doctor prescribes. Other forms of the drug are available over the counter (OTC). They’re used for nasal congestion and hemorrhoids. But this article focuses on the forms prescribed.

Common questions about phenylephrine

Below you’ll find answers to a few commonly asked questions about phenylephrine.

How does phenylephrine compare with pseudoephedrine?

Phenylephrine and pseudoephedrine are both prescribed to treat nasal congestion. However, pseudoephedrine is a stimulant drug. Stimulant drugs have the potential to be misused. Misuse means a drug is taken in a way other than how it’s prescribed.

If you’d like to know more about the differences between phenylephrine and pseudoephedrine, talk with your doctor or pharmacist.

What is phenylephrine’s mechanism of action? And how does the drug work?

How a drug works is called the mechanism of action. When used as an eye drop, phenylephrine works by making blood vessels in the eye narrower and relaxing muscles. This causes the pupils to become larger. Phenylephrine eye drops start working in about 15 minutes.

For treating low blood pressure, phenylephrine’s mechanism of action is to help blood vessels become narrower, which raises your blood pressure. This intravenous (IV) injection or infusion form of phenylephrine given into the vein starts working for this use within a few minutes.

If you’d like to know more about how phenylephrine works, talk with your doctor or pharmacist.

Side effects of phenylephrine

Phenylephrine may cause mild or serious side effects. More common mild side effects of phenylephrine and its serious side effects are listed below. This article doesn’t include all possible side effects of the drug. Side effects can vary based on your age, overall health, and any other medications you take.

To learn more about phenylephrine’s side effects, ask your doctor or pharmacist. You can also refer to the prescribing information for phenylephrine listed in the “Resources” section.

Mild side effects

More common mild side effects reported with some forms of phenylephrine are listed below. These side effects may differ based on the form of phenylephrine you take.

This article doesn’t include all possible mild side effects of the drug. To learn more about phenylephrine’s side effects based on the form, refer to the prescribing information for phenylephrine listed in the “Resources” section.

With many drugs, mild side effects may go away within a few days or a couple of weeks. If the side effects are bothersome, tell your doctor or pharmacist. They may be able to suggest ways to manage them.

Phenylepinephrine intravenous (IV) injection or phenylepinephrine infusion’s mild side effects include:

• nausea
• vomiting
• headache
• blurry vision
• mild allergic reaction*

Phenylephrine eye drops’ mild side effects include:

• temporary stinging and burning of the eyes
• blurry vision
• light sensitivity
• increased blood pressure
• mild allergic reaction*

* For details about this side effect, see the “Interactions and warnings for phenylephrine” section.

Serious side effects

Serious side effects of phenylephrine are listed below. These side effects may differ based on the form of phenylephrine you take.

This article doesn’t include all possible serious side effects of the drug. To learn more about phenylephrine’s side effects based on the form, refer to the prescribing information for phenylephrine listed in the “Resources” section.

With many drugs, serious side effects are possible but not common. If you have serious side effects from this drug, call your doctor right away. If you’re having severe symptoms or a medical emergency, call 911 or a local emergency number.

In general, phenylephrine’s serious side effects include: 

• fast, slow, or irregular heartbeat
• heart-related side effects, including heart attack, with phenylephrine drops
• lack of blood flow and oxygen to body parts and organs with phenylephrine (IV)
• high blood pressure, including hypertensive emergency, with phenylephrine (IV)
• severe allergic reaction*

* For details about this side effect, see the “Interactions and warnings for phenylephrine” section.

Uses of phenylephrine

The Food and Drug Administration (FDA) approves prescription drugs such as phenylephrine for certain conditions. Approved uses for phenylephrine are described below. These uses differ based on the form of phenylephrine prescribed.

Use for low blood pressure

Doctors may prescribe phenylephrine intravenous (IV) injection or infusion into the vein for treating low blood pressure. It’s prescribed for this purpose in people ages 1 year and older. It’s usually prescribed as a short-term treatment in the hospital.

Phenylephrine is mostly used when a patient’s blood pressure gets too low while they are under anesthesia. Low blood pressure can be life threatening. Doctors use phenylephrine to treat low blood pressure during surgery and in other emergency situations.

Use for pupil dilation

Doctors may prescribe phenylephrine eye drops for treating certain eye conditions. It’s used for this purpose in people of all ages. It can be prescribed as a short-term or long-term treatment.

Phenylephrine eye drops are used to make the pupils larger during eye exams or operations on the eye. It can also be used for other medical conditions based on your doctor’s decision.

Interactions and warnings for phenylephrine

Below, you’ll find information about phenylephrine’s possible interactions and warnings.

Interactions of phenylephrine

Certain things may affect how a drug works. These include getting vaccines, consuming alcohol or certain foods, or taking the drug with other medications. This effect is called a drug interaction.

Before you take phenylephrine, ask your doctor to check for possible interactions. Be sure to tell them about any of the following you take or use:

• prescription or over-the-counter drugs 
• vitamins, herbs, or supplements

To learn about drug-condition interactions, see the “Warnings for phenylephrine” section below.

Warnings for phenylephrine

Some people should not take phenylephrine, and others should take it cautiously.

Phenylephrine could cause harm to people with certain health conditions. This effect is called a drug-condition interaction. Other factors can also affect whether phenylephrine is a safe option for you. These warnings may differ based on the form of phenylephrine you take.

Ask your doctor about specific warnings for phenylephrine, and be sure to tell your doctor about your:

• current health, including any allergies to medications
• past health conditions or surgeries

Allergic reaction

Phenylephrine can cause an allergic reaction in some people. Severe allergic reactions are rare but possible.

If you’ve had an allergic reaction to phenylephrine or any of its ingredients, your doctor will likely not prescribe phenylephrine. They can tell you about medications that are safer options for you.

A mild allergic reaction may cause the following symptoms:

• skin rash
• itchiness
• flushing (temporary warmth, redness, or deepening of skin color)

A severe allergic reaction may cause the following symptoms:

• swelling under your skin, usually in your hands, feet, eyelids, or lips
• swelling of your mouth, throat, or tongue, which can cause breathing problems

If you have an allergic reaction to phenylephrine, call your doctor right away. If you have severe symptoms, call 911 or a local emergency number.

Overdose of phenylephrine

If you take phenylephrine, you should not take more phenylephrine than your doctor prescribes. For some drugs, doing so may lead to harmful effects or overdose.

If you think you’ve taken too much phenylephrine, call your doctor or pharmacist right away. Or you could call 800-222-1222 to speak with someone at America’s Poison Centers. You can also use its online resource. If you have concerning symptoms, call 911 or a local emergency number immediately. You can also go to the closest emergency room.

Pregnancy or breastfeeding and phenylephrine

Information about phenylephrine and pregnancy and breastfeeding is described below.

Phenylephrine and pregnancy

It’s not known whether phenylephrine should be taken during pregnancy. If you’re planning a pregnancy or can become pregnant, talk with your doctor before taking this medication.

Phenylephrine and breastfeeding

It’s not known whether phenylephrine should be taken while breastfeeding. If you’re breastfeeding or planning to do so, talk with your doctor before taking this medication.

What to ask your doctor

Let your doctor know if you have questions about phenylephrine or would like more details about it.

Here’s a list of some possible questions you may want to ask your doctor:

• Am I at higher risk of side effects than others?
• Are there long-term side effects of taking phenylephrine?
• Are there any alternative medications that you can prescribe for my condition?

Resources

• Food and Drug Administration. (2023). Orange Book: Approved drug products with therapeutic equivalence evaluations. https://www.accessdata.fda.gov/scripts/cder/ob/index.cfm   
• Phenylephrine hydrochloride injection. (2023). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/303bc1e6-0735-4ea1-84cd-6c1b621de0ed/spl-doc
• Phenylephrine hydrochloride solution/drops. (2023). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/a4d3fe20-f063-11e0-ac29-0002a5d5c51b/spl-doc

Disclaimer: Optum Perks has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.