What Can Cause False Positives for Drug Test?

People may be asked to take a drug test for a few different reasons. One of the most common reasons is for employment.  Drug screens check a person’s system for the presence of drugs or illegal substances. However, it is possible for a test to have a false positive result.   Knowing what a false positive is and how to avoid this problem can be important for anyone expecting to take a drug screening.

What does False Positive Mean?

The phrase “false positive” refers to results on a drug screening that say the test detected the presence of a substance when a person has not actually taken the substance.  Certain foods, medications, or other substance can cause a false positive reading. . False positives are not common in drug screenings, but they are possible.

Drug tests may screen for marijuana (THC), opiates, cocaine, amphetamines, methadone, steroids, barbiturates, benzodiazepines, phencyclidine (PCP), ecstasy, or more.

What Things Could Cause a False Positive?

It is important to know that these things will not always cause a false positive to appear on a drug test.  It depends greatly on what the test is screening for, how a test is processed, and how much of a substance someone has consumed.  As testing methods have improved, false positives have become much less common.

Poppy Seeds

Foods with poppy seeds, like some bagels, could cause a false positive for opioid screenings.  This is because poppy seeds naturally have small amounts codeine and morphine.


Some tests detect even a trace amount of alcohol.  Many products such as mouth wish, vanilla extract, and liquid medications, contain ethanol.  Ethanol is a simple grain alcohol.  The presence of ethanol may be detected in an alcohol urine screening.

Secondhand Marijuana Smoke

Right after a large amount of exposure to marijuana, THC may appear in a urine test.  However, modern tests are very unlikely to yield positive results from secondhand smoke.


While Cannabidiol (CBD) does not make people high, large amounts of consumption could lead to a positive THS urine test.

Cough Suppressants, Decongestants, and Sleep Aides

Over-the-counter cough suppressants, like Robitussin, includes an active ingredient Dextromethorphan.  This could cause false positives in tests for opiates and PCP.

Pseudoephedrine, or Sudafed, could cause false positives for amphetamine or methamphetamine.

Over-the-counter sleep aid drugs, like Unisom, may also lead to false positive results for PCP and methadone.

Weight Loss Pills

Some weight loss medications have caused false positives in amphetamine urine tests. Phentermine is one prescription that could cause this.

ADHD Medications

ADHD Medications, such as Ritalin (methylphenidate) are known to cause false positives tests for LSD, amphetamine, and methamphetamine.


Several different antidepressant medications have the potential to cause false positives. Other antidepressants not included in this list could also lead to false positive screenings. Be sure to speak to a medical professional about these medications when taking a drug test.

Quetiapine, known as Seroquel, could yield false positives for methadone or opiates.

Sertraline, known as Zoloft, could lead to false positives for benzodiazepine or LSD screenings.

Trazodone may also cause a false positive test for amphetamine, LSD, or methamphetamine.

Tricyclic antidepressants (TCA), such as Amitril, Norpramin, Zonalon, Prudoxin, or Tofranil, may lead to false positive urine tests for LSD.

Venlafaxine, known as Effexor XR, could learn to a false positive on a PCP urine test.


Levofloxacin and Ofloxacin are known as Quinolone antibiotics. These may cause false positives for opiate, amphetamine, or methamphetamine tests.

The antibiotic used to treat tuberculosis (Rifampin) could cause false positives for opioid urine screenings.

Pain or Anti-Inflammatory Medication

Tramadol or Ultram could register a false positive in opiate or PCP screenings

Ibuprofen, like Motrin or Advil, could lead to false positives for barbiturates, PCP, or THC. Aleve, or naproxen, may also lead to a false positive for barbiturates of THC.


Benadryl, Tylenol PM, Advil PM, and other medications contain diphenhydramine. This could lead to positive results in screenings for methadone, PCP, or opiates.

HIV Medication

False positives for marijuana screenings could occur as a result of taking Sustiva (Efavirenz). This is a antiretroviral medication used to treat HIV infection.

Antipsychotic Drugs

Chlorpromazine may cause false positives for amphetamine.

Quetiapine could lead to a false positive for methadone in a urine test.

Other Prescription Medications

Medications used to treat hypertension, such as Cardizem (Diltiazem) could lead to a false positive on a urine LSD test.

Metformin, a common prescription for diabetes treatment, has led to some positive results in tests for amphetamine or methamphetamine.

This may not be a complete list, as there are so many variables. If you have any questions about false positive substance results from a test, speak with a medical professional. Let the medical professional administering the screening know if you are taking any of these medications. If you experience what you believe to be a false positive, request a second drug screening test.