Estimates say that more than 2 million Americans rely on marijuana as part of medical treatment while around 18 million use the substance illegally for recreation. Because of these large numbers, it is no surprise that your chances of being exposed to second hand marijuana smoke are raising, whether or not you are aware of. This exposure leads many people to ask, can you test positive for THC from second hand smoke?

Could Second-Hand Marijuana Smoke Make You Fail a Drug Test?

The quick answer is that you are unlikely to have a second hand marijuana smoke drug test with a positive result. Marijuana smokers exhale very small amounts of THC, which means that to test positive on a drug test, you would need a great deal of secondhand exposure.

A 2010 study examined how secondhand marijuana smoke affected those who did not smoke. The non-smokers sat in a well-ventilated area that included people who were casually smoking marijuana and remained there for three hours. Following this, the researchers took a second hand marijuana smoke drug test, both via urine and blood samples. The non-smokers did have some level of THC in their systems, but it was significantly less than the amount they would have needed to fail the drug test. Another, later study recreated these results. Therefore we know that it is rare to test positive and it will most likely only occur within a few hours after your exposure.

Keep in mind, however, that failing a drug test from second hand marijuana smoke isn’t impossible since new tests are now more sensitive. You also have a small chance of a positive test result within several hours or a day following your exposure to marijuana.

About THC and Urinalysis

Urinalysis is the most common drug test. In this test, they take a small urine sample and test it for various drugs, including THC. A THC level of 50 ng/ml or more is considered a positive test result. The period of time that experts can detect marijuana in urine will depend greatly on how often the drug is used. Those who use marijuana more than one time a week will have levels that build up to more than 50 ng/ml in their urine. For them, it may take weeks or months to drop back down to underneath this level. If you are an occasional user, however, meaning you only use it one time a week or less, your levels will go back below 50 ng/ml in two or three days.

What Should You Do If You Have a Positive Result with Second-Hand Marijuana Smoke?

In cases where you haven’t smoked marijuana and your test is positive, you should ask for a follow-up urine test or blood test or make an appeal. Most of the time, a single urine test for the first screening is not seen as conclusive evidence that the active ingredient as well as metabolites are present. In this case, a confirmation test will be done. Remember, however, that individual organizations may have varying policies concerning drug use and second hand marijuana smoke drug test results.

Always limit your exposure to even second hand marijuana smoke as the harmful effects may still impact you, even when you are a passive smoker.

What Are the Effects of Inhaling Second-Hand Marijuana Smoke?

Researchers are still unsure of the extent of the effects of inhaling second hand marijuana smoke. We aren’t sure how you will be affected if you live with someone who regularly smokes marijuana, or if the higher levels of THC found in many marijuana cigarettes has an impact on second hand smoker.

There was a recent study done on rats suggests that the rats exposed to secondhand marijuana smoke will affect your blood vessels and heart as negatively as it would with secondhand tobacco smoke. The results haven’t been extended to humans, however.

We do know that marijuana smoke contains cancer-causing, harmful chemicals just like tobacco smoke. We still need to do more research, though, in order to find out the health effects in the long run.

How Long Does Marijuana Stay in Your System?

The most common options for first or second hand marijuana smoke drug tests are testing hair, saliva, or urine. The detection time will vary by the type of test. Because urine’s detection time is longer than that of saliva and it is cheap, it is the most commonly used.

Other factors that affect the length of time THC will remain in your system include frequency of use, amount used, body fat, and weight. As these factors vary greatly by person, you won’t find specific guidelines for the amount of time marijuana stays in your system.

THC is positive in urine drug tests for 2 to 5 hours within use. After this, the amount of time it remains can be estimated by frequency of use. Keep in mind, however, that these estimates don’t account for body fat or weight.

  • One time users may be positive from 1 to 6 days

  • Moderate users may be positive from 7 to 13 days

  • Frequent users may be positive for 15 days or more

  • Heavy users may be positive for 30 days or more

  • Some heavy users may be positive for 45 to 90 days

For saliva tests, THC will always be positive for an hour after using, but may be negative within 12 hours.

Hair drug tests usually show THC from 7 days after last use up to 90 days. This testing method isn’t widely considered accurate, however, as THC won’t always bind to hair follicles.

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