Introduction

There are times in life when you need to pee in a cup. For example, you may need to take a drug test before starting a new job. But these tests aren’t foolproof: A number of harmless, common substances can trigger a false positive for drugs. Here’s a look at nine substances that can give you an unusual positive for illegal drugs.

Coca tea

Drinking coca tea could cause a false positive result for cocaine. The tea is popular in South America and is made from the leaves of the coca plant, the same source that cocaine is made from. In a 2006 study, five people drank coca tea before taking a drug test. All participants tested positive for cocaine metabolites two hours after consuming the tea, and three participants were still positive after 36 hours. The researchers concluded that “healthcare professionals should consider a history of coca tea ingestion when interpreting urine toxicology results.”

Cold Medicines

Some over-the-counter cold medications contain ingredients that could cause a false positive for amphetamines. For example, the ingredient brompheniramine, which is an antihistamine in some cold and allergy medications, can interfere with the methamphetamine test, leading to false positive results, according to a 2010 study. And in the past, use of the nasal decongestant Vick's Inhaler has led to false positives for amphetamines, according to a 2008 study. Vick's inhaler contains levomethamphetamine, which is a chemical "mirror image" of methamphetamine, the authors of that study wrote. However, newer drug tests can distinguish between methamphetamine and the chemical in Vick's inhaler, so the cold medicine no longer triggers false positives, the study said.

Secondhand marijuana smoke

In extreme cases, being in a room with someone who smokes marijuana can cause a positive result on a marijuana drug test, according to a 2015 study. In that research, six people smoked marijuana in a sealed room while six nonsmokers sat next to them. After an hour, several of the nonsmokers tested positive for marijuana on sensitive tests that could detect tetrahydrocannabinol, or THC (the active ingredient in marijuana), at concentrations of 20 to 50 nanograms per milliliter.

The researchers concluded that "these results demonstrate that extreme exposure to cannabis smoke can produce positive urine tests at concentrations commonly used as thresholds." However, the researchers noted that such positive tests in real-world settings are likely rare, as testing would have to be done within hours of exposure, and nonsmokers would likely be aware that they had been exposed to secondhand marijuana smoke.

Antibiotics

Some antibiotics, including rifampin and fluoroquinolones, can cause false-positive results for opiates. In one case reported in 2002, a 7-year-old boy in Lebanon who went to the emergency room tested positive for opiates. However, it was later determined that the rifampin he was taking had interfered with his drug test.

Baby soap

Some soaps used in hospitals to wash babies shortly after birth can cause infants to test positive for marijuana on certain newborn screening tests, according to a 2012 study. (These tests are done to determine whether a mother was using drugs during pregnancy.) Health care workers have found that babies washed with these soaps — including the Johnson & Johnson's Head-to-Toe Baby Wash, le J&J Bedtime Bath, le CVS Night-Time Baby Bath, l'Aveeno Soothing Relief Creamy Wash et l'Aveeno Wash Shampoo — tested positive on a urine drug test for THC, the active compound in marijuana.

The researchers in this study said they don't know why the soaps cause a false positive. It could be that some of the compounds in the soap are structurally similar to THC, or that chemicals in the soap alter the way the test works, they said. As for how the soap got into the urine sample, the researchers suspect that soap residue on the babies' skin washed into the child's urine sample.

Ibuprofène

Taking nonsteroidal anti-inflammatory drugs, such as ibuprofen, can, in rare cases, cause a false positive for several drugs. In a 1990 study, 60 people took ibuprofen at different doses (a single dose of 400 mg per day, three doses of 200 mg per day, or three doses of 400 mg per day, depending on which treatment group they were in). One patient taking the highest dose of ibuprofen (1,200 mg per day) tested positive for cannabinoids, a compound in marijuana. Another patient tested positive for barbiturates, which are used in anti-anxiety or sleep medications. The results "demonstrate the low probability of a false positive [test]" after taking ibuprofen, the researchers concluded.

Tonic water

Tonic water contains small amounts of quinine, a drug used to treat malaria. Quinine is also sometimes mixed with street drugs, and so it can be an indicator of illegal drug use. In a 1989 study, researchers at Brown University in Rhode Island reported that a positive urine test for quinine was due to drinking tonic water in a cocktail..

HIV Medication

An antiviral drug used to treat HIV can also cause people to test positive for marijuana. For example, in 2006, researchers reported interesting results from a study of 24 people taking the HIV drug efavirenz (brand name Sustiva). At the start of the study, all of the participants tested negative for THC, but after taking efavirenz, they all tested positive. The researchers said that efavirenz might interfere with how the test works.

Poppy seeds

Poppy seeds naturally contain compounds called morphine and codeine, so consuming certain products with poppy seeds can trigger false-positive results for these drugs. In a 1987 study, five members of a lab baked cookies containing about a teaspoon (5 milliliters) of poppy seed filling that they had purchased at the supermarket. Two hours after eating several cookies, all members of the lab tested positive for opiates. The drug concentration was above 300 ng/mL, which was the minimum threshold used by the test.

In 1998, the Department of Health and Human Services changed the threshold to 2,000 ng/mL to prevent false-positive results from poppy seed consumption, according to a 2008 study. However, most labs continue to use lower thresholds, the researchers in that study said.

Source:LiveScience