What can cause a false positive drug test?

1. Dextromethorphan (Robitussin, Delsym)

Dextromethorphan is the main ingredient in many OTC cough suppressants. If you’ve taken dextromethorphan, a urine test may show positive for PCP.

2. Diphenhydramine (Benadryl)

Diphenhydramine is an antihistamine that can help treat allergies, itching, and cold symptoms. Diphenhydramine may cause a false positive result for some opioids and opiates. But it’s not clear what dose of diphenhydramine would cause a false positive result. Typical doses of diphenhydramine may not cause a false positive result.

Some reports have also shown that diphenhydramine may turn a drug test positive for PCP. But this is rare. 

3. Certain decongestants

Used for sinus and nasal congestion, pseudoephedrine (Sudafed) may cause false positive test results for amphetamine or methamphetamine. 

4. Phentermine

Phentermine (Adipex-P) is FDA-approved to help some people lose weight. It works by lowering your appetite. Taking phentermine can cause false positive urine test results for amphetamines.

5. NSAIDs

Ibuprofen (Motrin, Advil) and naproxen (Aleve, Naprosyn) are in a group of medications called nonsteroidal anti-inflammatory medications (NSAIDs). They’re used to help treat fever, inflammation, and pain. If you take either of these OTC NSAIDs, there’s a small chance your urine test may be positive for barbiturates (a type of sedative) or THC. 

Another NSAID, oxaprozin (Daypro), can be used to treat pain from arthritis. Taking oxaprozin may result in a false positive test for benzodiazepines.

6. Some antidepressants

Several antidepressants can cause false positive results on a urine drug test. Examples include:

• Venlafaxine (Effexor XR) and desvenlafaxine (Pristiq) are part of a group of antidepressant medications called serotonin-norepinephrine reuptake inhibitors (SNRIs). Taking either of these medications may result in a false positive for PCP.

• Sertraline (Zoloft) is a selective serotonin reuptake inhibitor (SSRI). Sertraline can cause a positive result for the hallucinogen LSD on a urine drug test. It may also cause a positive result for benzodiazepines.

• Trazodone is an older antidepressant that's not commonly used for depression anymore. Taking trazodone may cause a false positive test result for amphetamine or methamphetamine.

• Bupropion (Wellbutrin XL, Wellbutrin SR) may lead to false positive results for amphetamine or methamphetamine.

7. Quetiapine

Atypical antipsychotics can help treat certain mental health conditions like bipolar disorder and schizophrenia. Quetiapine (Seroquel) is one type of atypical antipsychotic. It could cause you to test positive for opioids (specifically methadone). 

8. Proton pump inhibitors

Proton pump inhibitors (PPIs) can treat gastroesophageal reflux disease (GERD) and heartburn symptoms. Taking PPIs — specifically pantoprazole (Protonix) — may cause false positive results for THC.

9. Quinolone antibiotics 

Quinolone antibiotics treat many bacterial infections. Levofloxacin (Levaquin) and ofloxacin are the most likely of the quinolone antibiotics to cause a false positive urine test for opiates. Ofloxacin may also cause a false positive result for amphetamine or methamphetamine.

10. Promethazine

Promethazine is part of a group of medications called phenothiazines. It can be used to help relieve nausea and vomiting. It can cause false positive results for amphetamine or methamphetamine. 

Rare (but possible) medications that can cause false positives

There are a few other medications that may rarely cause false positives. These include labetalol (Trandate), doxylamine (Unisom), and tramadol (Ultram).

Labetalol

Labetalol is in a group of medications called beta-blockers. It helps lower blood pressure in people with high blood pressure (hypertension). While rare, labetalol could cause a false positive test for amphetamine or methamphetamine. 

Doxylamine

Doxylamine is an OTC medication that may help people struggling to fall asleep at night. Large doses of doxylamine can cause a false positive for opioids (specifically methadone).

Tramadol

Tramadol is an opioid medication that treats pain. Your drug screen could become positive for methadone or PCP with large doses of tramadol.

Debunked: Does methylphenidate cause false positives for amphetamine?

Methylphenidate is a stimulant medication used to treat ADHD. Many sources state that methylphenidate can cause false positive results for amphetamines.

But research shows this isn’t true. If you’re prescribed methylphenidate for ADHD, you shouldn’t have to worry about having a positive drug result for amphetamines. 

What should I do if I get a false positive result on a drug test?

If you think you’ve had a false positive on a urine drug test, consider whether any medications you take could be responsible. 

Then talk to your healthcare provider. They may be able to confirm the results by running a second test. Confirmation tests are more specific for the substance or medication in question. The results of a confirmation test are much less likely to show false positive results.

In some cases, though, running a second test may not be possible. Talk to your provider if you’re concerned about false positive test results.