You may know pseudoephedrine and phenylephrine from their use in Sudafed products. Sudafed contains pseudoephedrine, while Sudafed PE contains phenylephrine. The drugs are also available in several combinations with other over-the-counter cough and cold medications. These drugs are both nasal decongestants. They’re used for short-term relief of congestion and pressure in the sinuses and nasal passages caused by the common cold, hay fever, or other allergies. If you’re ready to breathe easier, check out this comparison of pseudoephedrine and phenylephrine.

The chart below is a quick snapshot of some of the basic information for pseudoephedrine and phenylephrine.

PseudoephedrinePhenylephrine
What’s the brand-name version?SudafedSudafed PE
Is a generic version available?yesyes
Why is it used?short-term relief of sinus or nasal congestion and pressureshort-term relief of sinus or nasal congestion and pressure
Does it require a prescription?in Oregon, Mississippi, and some cities in Missouri and Tennesseeno
Are there special requirements for purchase?yes no
What form(s) does it come in?• oral tablet
• oral liquid
• oral extended-release (long-acting) tablets, 12-hour and 24-hour forms
• oral tablet
• oral liquid
• nasal spray
What are the strengths?• 30 mg
• 60 mg
• 120 mg
• 3–6 mg/mL
• 10 mg
• 0.5–10 mg/mL
How often should I take it?• oral tablet or liquid: every 4–6 hours
• 12-hour extended-release tablet: once every 12 hours
• 24-hour extended-release tablet: once every 24 hours
up to every 4 hours as needed
How long it can be taken?up to 7 days in a row• oral forms: up to 7 days in a row
• nasal form: up to 3 days in a row
Is it safe for children?safe for children 4 years and older* safe for children 4 years and older
Does it have potential for misuse?yes**no
* Except for the extended-release tablets, which are only safe for children 12 years and older
** Pseudoephedrine itself is not addictive. However, the illegal methamphetamine that it can be used to make is highly addictive.

You can walk into any pharmacy and buy phenylephrine off the shelf like you would for any other purchase. But for pseudoephedrine, there are special requirements. To get it, you have to buy it from the pharmacy staff, not off the shelf. You also have to show ID, and you’re limited in the amount you can buy daily and monthly. The reason for these requirements is that pseudoephedrine is used to make illegal methamphetamine, which is highly addictive. These rules help prevent people from buying products that contain pseudoephedrine to make methamphetamine.

Studies in 2006 and 2009 found pseudoephedrine to be more effective than phenylephrine in the treatment of nasal congestion.

Both pseudoephedrine and phenylephrine can cause side effects. Call your doctor if you have any serious side effects when using these drugs.

The chart below lists examples of possible side effects from pseudoephedrine and phenylephrine.

Common side effectsPseudoephedrinePhenylephrine
restlessness
sleeping trouble
nausea
vomiting
Serious side effectsPseudoephedrinePhenylephrine
extreme sleeplessness
nervousness
dizziness
breathing trouble
fast or abnormal heartbeat
stomach pain

An interaction is when a substance changes the way a drug works. This can be harmful or prevent the drug from working well. Before starting pseudoephedrine or phenylephrine, tell your doctor about all medications, vitamins, or herbs you’re taking. This can help your doctor prevent possible interactions.

Don’t use with MAOIs

One class of drugs that is known to interact with both pseudoephedrine and phenylephrine is monoamine oxidase inhibitors (MAOIs). This class includes drugs such as:

  • isocarboxazid
  • phenelzine (Nardil)
  • selegiline
  • tranylcypromine (Parnate)

If you’re taking an MAOI, do not take pseudoephedrine or phenylephrine. Ask your doctor about other treatment options.

Don’t use them together

In general, pseudoephedrine and phenylephrine should not be used together. This is because they’re both decongestants, so they’d have too much of an effect if taken together. Combining them could lead to increases in both blood pressure and heart rate. However, check with your doctor. In some cases, you may be able to try pseudoephedrine two to three hours after your last dose of phenylephrine if you didn’t have symptom relief with phenylephrine.

Certain medications can make certain conditions or diseases worse. If you have any of the following conditions, you should discuss with your doctor before taking pseudoephedrine or phenylephrine:

  • heart disease
  • high blood pressure
  • diabetes
  • thyroid disease
  • enlarged prostate gland

If you want to take pseudoephedrine, you should also talk to your doctor if you have:

  • glaucoma

Pseudoephedrine and phenylephrine can both affect pregnancy and breastfeeding.

These drugs are category C drugs, which means there’s the possibility of birth defects. Women should avoid using them during the first trimester of pregnancy and possibly throughout pregnancy. These drugs also pass into a woman’s breast milk, though phenylephrine does so in smaller amounts. That means these drugs may have side effects in a child who is breastfed by someone who takes these drugs. For example, pseudoephedrine may cause irritability and sleep changes in the child. In the mother, both drugs may decrease milk production.

If you’re pregnant or breastfeeding, talk with your doctor before using either of these drugs. Other treatments, such as oxymetazoline or the nasal form of phenylephrine, may be better options for you when you’re breastfeeding.

While pseudoephedrine and phenylephrine are similar in many ways, they also have some real differences. These include:

  • how effective they may be
  • how often you take them
  • how you access them
  • their risks of misuse

If you’re trying to decide which option might be better for you, talk with your doctor or pharmacist. They can help you determine if pseudoephedrine, phenylephrine, or another drug would be a good choice for you.