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What medicines may register false positives in drug tests?

Posted on April 30, 2021

You might be in the process of applying for a job or law enforcement may approach you on suspicion that you have illegal drugs in your possession. Whatever the situation, a drug test may be in your future. While a test might show that you have not ingested illegal substances, it could cause you problems if it produces a false positive.

The problem may be the medication you take. WebMD explains that some legal medicines may test positive for different kinds of illegal drugs.


If you suffer from an allergy or a head cold, you probably will head to your pharmacy for an antihistamine. But while one of these medicines may relieve your runny nose, it could also register positive for drugs. Sometimes allergy and sleep medicines produce positive results for a drug called methadone. A drug test may also mistake diphenhydramine for PCP, which is a hallucinogenic drug.


You might take antibiotics to treat an infection. If so, there is a slight risk that the antibiotics in your system may produce a false positive. Sometimes a test mistakes the antibotic Rifampin for an opiate. A false positive may even show up 18 hours past when you have ingested some of the antibiotic.

Drugs that treat mental illness

Some medicines that treat emotional disorders or mental conditions may also test positive for drugs. Doctors may prescribe Sertraline to treat panic attacks and obsessive compulsive disorders, but sometimes a drug test may not distinguish this kind of medicine from an illegal substance. Similarly, the antipsychotic medicine chlorpromazine may register a false positive for amphetamine.

Other medicines

There are other medications and treatments that at times create false positives. Weight loss pills might test positive for amphetamines. Efavirenz, which people use to treat HIV, may register as marijuana. To avoid the appearance of taking illegal drugs, you may have to explain your medical history to your employer or anyone who requires you to take a drug test to avoid confusion and possible legal entanglements.