Drugs Home > What Is the Half Life of Phenergan?

Phenergan® (promethazine hydrochloride) is a prescription medicine used for treating various conditions, including nausea and vomiting, motion sickness, and allergies. There have been reports that this medication can cause false positives on urine drug tests for amphetamines. For this reason, people may wonder about the half-life of Phenergan.
The elimination half-life of a medication is the time it takes for the blood levels of the drug to be reduced by half. The elimination half-life of Phenergan is approximately 10 to 19 hours. This means that every 10 to 19 hours, the level of medicine in your blood will drop by 50 percent of the previous level. In general, Phenergan will be mostly out of your system in two to four days.
(Click How Long Does Phenergan Stay In Your System? for more information on how to calculate the half-life of Phenergan and to find out why the medicine may cause false positives on drug tests.)
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Last reviewed by: Kristi Monson, PharmD;
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