Licescience explains how there are times in life when you just have to pee into a cup. For example, you might need to take a drug test before you start a new job.

However, these tests aren’t foolproof: A number of harmless, everyday substances can trigger a false-positive result for drugs. Here’s a look at nine substances that can give you an odd positive result for illegal drugs.

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1. Coca tea

Drinking coca tea could lead to 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 from which cocaine is derived.

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2. Cold medications

Some over-the-counter cold medications contain ingredients that could lead to a false-positive result for amphetamines. For example, the ingredient brompheniramine, which is an antihistamine in some cold and allergy medications, can interfere with the test for methamphetamine, leading to false-positive results, according to a 2010 review study.

And in the past, use of the nasal decongestant Vick’s Inhaler led to false positives for amphetamines, according to a 2008 review study. Vick’s inhaler contains levomethamphetamine, which is a chemical “mirror image” of methamphetamine, the authors of that review wrote. However, newer drug tests can distinguish between methamphetamine and the chemical in Vick’s inhaler, so the cold medication no longer triggers a false positive, the review said.

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3. Secondhand smoke from marijuana

In extreme cases, being in a room with someone who is smoking marijuana can lead to a positive result on a marijuana test, according to a 2015 study.

Extreme cannabis smoke exposure can produce positive urine tests at commonly utilized cutoff concentrations. However, the researchers noted that these positive tests in real-world settings are likely to be rare, because testing would need to occur within hours of the exposure, and nonsmokers would likely be aware that they had been exposed to secondhand marijuana smoke.

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4. Antibiotics

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

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5. Baby soap

Certain soaps used in hospitals to wash babies shortly after birth may cause the infants to test positive for marijuana on some newborn screening tests, according to a 2012 study. (Such tests are done to determine if a mother was using drugs while pregnant.)

Health care workers figured out that babies who are washed with these soaps — which include Johnson & Johnson’s Head-to-Toe Baby Wash, J&J Bedtime Bath, CVS Night-Time Baby Bath, Aveeno Soothing Relief Creamy Wash and Aveeno Wash Shampoo — gave a positive result on a urine drug screening test for THC, the active compound in marijuana.

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6. Ibuprofen

Taking nonsteroidal anti-inflammatory drugs, such as ibuprofen, can, in rare cases, lead to a false-positive result for several drugs.

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7. 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 result on a urine test for quinine resulted from the consumption of tonic water in a mixed drink.

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8. HIV medication

An antiviral medication used to treat HIV can also cause people to test positive for marijuana. For example, in 2006, researchers reported interesting findings from a study of 24 people who took the HIV medication efavirenz (brand name Sustiva). At the beginning of the study, all of the participants tested negative for THC, but after taking efavirenz, they all tested positive. Researchers said that efavirenz may interfere with the way the test works.

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9. Poppy seeds

Poppy seeds naturally contain the compounds morphine and codeine, and so consumption of some products with poppy seeds can trigger false positives results for these drugs. In a 1987 study, five members of a lab baked cookies containing about 1 teaspoon (5 milliliters) of a poppy-seed filling that they bought from the grocery store. Two hours after eating several cookies, all of the lab members tested positive for opiates. The concentration of the drug was greater than 300 ng/mL, which was the minimum cutoff used by the test.

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