How Long Does Sudafed PE (Phenylephrine) Stay In Your System?

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!