How Long Does Sudafed PE (Phenylephrine) Stay In Your System?
In our latest question and answer, the pharmacist discusses how long 'Sudafed PE' (phenylephrine) stays in your system.
Hello, how long does phenylephrine nasal congestion stay in the urine? I think it caused a false-positive drug test.
Oct 24, 2022- Phenylephrine stays in your system for approximately 12 to 18 hours after your last dose in most healthy adults.
- Phenylephrine can cause a false positive result on urine drug screens for amphetamines due to its structural similarity to those drugs.
- If you get a false positive result, inform your doctor and the testing company about all medications and supplements you are taking, and ask about more accurate confirmatory tests like gas chromatography or mass spectrometry.
Answer
Hi Star and thank you for your question. I give more detail in the next sections, but for most healthy adults, based on the known half-life of phenylephrine (2.5-3 hours), it will stay in your system between 12 and 18 hours after your last dose.
Information On Urine Drug Screens
Urine drug screens are a very useful tool for health care professionals, but they can sometimes be a bit problematic as we sometimes get false positives.
False-positives can occur because they typically aren’t looking for a specific drug in your urine. Instead, they are usually looking for a known metabolite to react with an antibody. Due to this, sometimes an unrelated drug may cause a reaction, and thus, a false-positive result.
Most labs or testing companies will have a reference file of drugs that may cause a false positive. It’s always a good idea to provide the lab or your physician with a list of medications that you are presently taking, as well as any over-the-counter herbals or supplements.
Phenylephrine Causing False-Positives
One common over-the-counter drug that can cause a false positive urine drug test is the nasal decongestant phenylephrine (as well as the similar nasal decongestant pseudoephedrine) due to its structural similarity to amphetamines.
Several different reports and studies exist that establish a link between using it and registering a false positive for amphetamines / methamphetamine (including this one from the Mayo Clinic).
How Long Is Phenylephrine Detectable On A Urine Drug Screening?
Phenylephrine has a half-life of about 2.5-3 hours, which means that your body eliminates half of the dose within about 3 hours.
Most drugs begin to be undetectable within about 5 or 6 half-lives. Based on this, I would assume that phenylephrine metabolites would be detectable in your urine for up to 12-18 hours after your last dose (assuming you are taking an immediate-release product).
What To Do About A False-Positive Result
If you feel you received a false positive test result, be sure to talk to your doctor and tester about all the drugs and supplements you take. They should be aware of drugs that can conflict with these tests.
Additionally, there are more accurate tests available than urine drug screenings. Gas chromatography, mass spectrometry, or d/l isomer tests all can distinguish between a false positive and true positive test since they detect actual compounds in a given sample, and do not rely on antibody reactions.
These additional tests tend to be expensive and may not be covered under your insurance though.
Final Words
I hope that helps and feel free to write to us in the future!
References & sources
- Phenylephrine Monograph — PubChem
- Urine Drug Screening: Practical Guide for Clinicians — Mayo Clinic
- Immunoassay cross-reactivity of phenylephrine and methamphetamine — PubMed
Glossary — Terms in This Answer
- Half-life
- The amount of time it takes for your body to eliminate half of a dose of a drug.
- Metabolite
- A substance produced when your body breaks down and processes a drug.
- False positive
- A test result that incorrectly shows the presence of a drug when you haven't actually taken it.
- Antibody
- A protein in your body that reacts with specific substances; urine drug tests use antibodies to detect drugs.
- Phenylephrine
- A common over-the-counter nasal decongestant used to relieve congestion.
- Amphetamines
- A class of stimulant drugs that phenylephrine can resemble structurally, leading to false positive test results.
- Gas chromatography
- A laboratory test that separates and identifies actual drug compounds in a sample with high accuracy.
- Mass spectrometry
- An analytical technique that measures the mass of molecules to precisely identify drug compounds in a sample.
Dr. Brian Staiger, PharmD
Doctor of Pharmacy, board certified clinical pharmacist (BCPS), American Herbalist Guild, Medication Therapy Management certified
Brian Staiger, PharmD, BCPS, is a licensed pharmacist with more than 13 years of experience across retail pharmacy, clinical pharmacy, medication safety, pharmacy program development, and healthcare administration. He is the founder of HelloPharmacist.com, where he helps patients...
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