How Long Does Phenergan Stay in Your System?

Phenergan can remain in the body between 2 and 4 days, according to eMedTV. This is due to this medication's half-life, which is 10 to 19 hour after taking a dose. Because this is an estimated time period, it is possible to test positive if someone takes certain types of drug screening tests.

Although this drug is not typically screened for in a drug test, it may present a positive result for amphetamine in rare instances, notes eMedTV. A drug's half-life is defined as the time it takes for the blood content to be half of the initial drug level.

Phenergan is the brand name of a drug used in the treatment of allergies, nausea, vomiting and difficulty sleeping, states RxList. Other possible uses for this oral medication, which is available under the generic name promethazine, are motion sickness and as a sedative. Minor side effects include dizziness and constipation, while serious ones include allergic reactions, breathing or heart problems, convulsions or fainting; the latter symptoms may require the immediate attention of a doctor or emergency care.

Drug interactions are possible if Phenergan is taken with medications such as sedatives, antidepressants and muscle relaxers, warns RxList. Patients should also follow their doctor's precise dosing instructions to avoid potential problems.