Pseudoephedrine: what it treats, how to take it, side effects
Last updated September 3, 2026.
Pseudoephedrine is a decongestant that shrinks swollen nasal blood vessels so you can breathe again. You may know it as Sudafed - the one sold from behind the pharmacy counter. It relieves congestion symptoms; it does not treat their cause or speed recovery.
What does it treat?
Nasal congestion caused by colds, allergies, and hay fever, plus temporary relief of sinus congestion and pressure. The Sudafed label says the same in drug-facts language. MedlinePlus notes a second, less-known use: it is sometimes taken to prevent ear pain and blockage from pressure changes during air travel or diving - a conversation to have with your doctor or pharmacist.
How do you take it?
Regular tablets and liquid run every 4 to 6 hours; the 12-hour extended-release tablet (120 mg) is 1 tablet every 12 hours with no more than 2 in 24 hours; the 24-hour version is once a day, one per 24 hours. Swallow extended-release tablets whole - never break, crush, or chew them. Take the last dose of the day several hours before bedtime, because this drug can keep you up. If symptoms do not improve within 7 days or you develop a fever, stop and call your doctor. It is usually taken as needed, so missed doses are rarely an issue.
Side effects to know
- Common: restlessness, nausea, vomiting, weakness, and headache.
- Serious: nervousness, dizziness, difficulty sleeping, stomach pain, difficulty breathing, and a fast, pounding, or irregular heartbeat - call your doctor immediately for these. This is a stimulant-class drug, and your cardiovascular system is where overdoing it shows up first.
Who should not take it?
Anyone taking an MAO inhibitor or within two weeks of stopping one - the label makes that a do-not-use. MedlinePlus tells you to clear it with your doctor first if you have high blood pressure, glaucoma, diabetes, difficulty urinating from an enlarged prostate, or thyroid or heart disease, and to flag any narrowing or blockage of the digestive system before taking the 24-hour tablet. Children under 4 should never get these products, under 12 should never get the extended-release tablets, and caffeine makes the side effects worse, so ease off the coffee while you are taking it. If you are pregnant, planning pregnancy, or breastfeeding, tell your doctor first - and mention it before any surgery, including dental work.
When is it an emergency?
A fast, pounding, or irregular heartbeat, difficulty breathing, or chest pain after a dose means calling your doctor immediately or getting emergency care. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Why is Sudafed kept behind the pharmacy counter?
Because pseudoephedrine can be misused as a raw material to make methamphetamine, so US law requires it to be sold from behind the counter with ID and purchase limits. The medicine itself is the same decongestant it has always been - MedlinePlus describes it simply as a nasal decongestant that narrows blood vessels in the nasal passages.
Can I take pseudoephedrine with high blood pressure?
Not without your doctor's sign-off. MedlinePlus lists high blood pressure, heart disease, thyroid disease, diabetes, glaucoma, and an enlarged prostate as conditions to disclose before taking it, because a drug that narrows blood vessels and speeds the system up can aggravate all of them. Ask your doctor or pharmacist first.
Will pseudoephedrine keep me awake at night?
It can. MedlinePlus advises taking the last dose of the day several hours before bedtime to help prevent trouble sleeping, and difficulty sleeping is on its serious side effect list. Caffeine makes the stimulant effects worse, so cut back on coffee while you are taking it.
What is the difference between pseudoephedrine and phenylephrine?
Pseudoephedrine is the behind-the-counter decongestant with the dosing schedules and precautions above. Phenylephrine is the one that replaced it on open shelves in many products. MedlinePlus covers pseudoephedrine only; if your box says phenylephrine, you are holding a different drug with its own directions.
Can I take pseudoephedrine with an MAOI antidepressant?
No. The Sudafed label says do not use if you are taking a prescription MAOI (certain drugs for depression, psychiatric, or emotional conditions, or Parkinson's disease) or for 2 weeks after stopping one. If you are unsure whether your medication is an MAOI, ask your pharmacist before taking a single tablet.
Can I give pseudoephedrine to my child?
Not the extended-release tablets to anyone under 12, and not any nonprescription pseudoephedrine product to a child under 4 - MedlinePlus warns these products can cause serious side effects or death in young children. For ages 4 to 11, use the package's age chart and caution, and ask the child's doctor when unsure.