What Can Cause False Positives for Drug Test?

Many companies ask prospective employees to complete a drug test as part of the hiring process. Some employers may also screen their staff for drug use at random times to check their systems for the presence of illicit drugs or other illegal substances like marijuana (THC), opiates, cocaine, amphetamines, methadone, steroids, barbiturates, benzodiazepines, phencyclidine (PCP), ecstasy, and more.

However, drug tests are known for sometimes producing false positive results, which means that people who have not taken drugs may get a positive result after the screening. This could lead to someone losing their career for no real reason. Therefore, everyone who is expecting to complete a drug screening should take proper precautions to avoid this problem.

What Does It Mean to Get A False Positive?

When someone gets a “false positive” on a screening, the test detects the presence of a substance that isn’t really in someone’s body. As testing methods have improved over the years, there have been less cases of false positive results. While these outcomes are not common, they are still very possible today.

What Causes False Positives?

If someone eats certain foods, takes specific medications, or uses other substances before taking a drug test, they have a chance of seeing a false positive result. The substances below may or may not cause a false positive result on a drug test depending on how much of the substance a person consumed, how the test is processed, and what the test is screening for.

Poppy Seeds

Some bagels and other foods with poppy seeds could cause a false positive for opioid screenings. This is because poppy seeds naturally have small amounts of codeine and morphine.


Certain screenings can detect even the smallest amount of alcohol.  Many products such as mouth wash, vanilla extract, and liquid medications contain ethanol, which is a simple grain alcohol. The presence of ethanol may be detected in a urine test for alcohol use.

Secondhand Marijuana Smoke

If someone is exposed to a large amount of marijuana before completing a urine drug test, THC may be detected. 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 result on a urine test for THC.

Cough Suppressants, Decongestants, and Sleep Aides

Over-the-counter cough suppressants like Robitussin include an active ingredient called Dextromethorphan, which 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 like phentermine have caused false positives in amphetamine urine tests.

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.

  • 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 lead to a false positive on a PCP urine test.

Be sure to speak to a medical professional about these medications when taking a drug test.


Levofloxacin and Ofloxacin are known as Quinolone antibiotics. They may cause false positives for opiate, amphetamine, or methamphetamine tests. The antibiotic used to treat tuberculosis (Rifampin) could also 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 (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), an antiretroviral medication used to treat HIV infections.

Antipsychotic Drugs

Chlorpromazine may cause false positives for amphetamine. Quetiapine could lead to a false positive for methadone on 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 to consider when discussing drug tests and the potential for false positives. 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.

For more information about drug screenings and false positive results, contact our team of substance abuse treatment representatives by calling 866-345-2147.