Can Promethazine show up on a drug test? 

Can Promethazine show up on a drug test? 

Promethazine may show up on a drug test as a false positive for Amphetamines or Methamphetamine. Promethazine can also test positive for Lysergic acid diethylamide (LSD) (1). 

It may not cause a false-positive every time, but it should be considered a possibility. 

Promethazine is not a controlled drug itself and it is used for the management and treatment of nausea and vomiting, but it can cause a false positive because of improper accuracy of the testing procedure. 

The primary method of drug testing is urine immunoassay, which is not the most promising method of testing and is associated with causing false positive results. 

How long does Promethazine stay in your body? 

Promethazine has a half-life of about 12-15 hours, after which the initial concentration of the drug reduces to half. The remaining serum concentration of the drug further reduces to half within the next 12-15 hours. 

The process continues until the drug is completely washed out from your body. This could take 2 to 3 days to complete the process. 

How to avoid false positives caused by Promethazine? 

If you’re going for a standard drug test, it’s best to take your last Promethazine dose 3 to 4 days before that. 

However, if your symptoms are at their peak, I don’t recommend stopping the medication, but there isn’t any way to prevent a false positive while the drug is in your system. 

The best you can do is go for a more sensitive testing procedure, rather than a urine immunoassay. Drug testing techniques like Gas Chromatography – Mass spectroscopy (GC-MS) provide promising results and do not cause any false positives (2). 

The technique identifies the exact chemical present in your life. However, the procedure is quite expensive. Cheaper testing procedures don’t have that high accuracy and they can cause false positives. 

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Alyson Schwebach, Jennifer Ball. Urine Drug Screening: Minimizing False Positives and False Negatives to Optimize Patient Care. US Pharm. 2013;38(12):1-6. Available at:


Ramoo B, Funke M, Frazee C, Garg U. Comprehensive Urine Drug Screen by Gas Chromatography/Mass Spectrometry (GC/MS). Methods Mol Biol. 2016;1383:125-31. doi: 10.1007/978-1-4939-3252-8_15. PMID: 26660182. Available from: