Can You Pass a Marijuana Drug Test?

Written by

Lee Johnson

Lee Johnson is the senior editor at CBD Oracle, and has been covering science, vaping and cannabis for over 10 years. He has a MS in Theoretical Physics from Uppsala...

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Medically reviewed byAbraham Benavides, MD

Medically reviewed by

Abraham Benavides, MD

Dr. Abraham Benavides is an international cannabis science advisor, health coach, and full-tuition merit scholar of the GW School of Medicine. Abe pioneered and published first-author research with the Cannabis...

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Using fake urine to pass a drug test for marijuana
Photo: University of Mississippi Medical Center
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If you’ve got a drug test coming up and you’re pretty sure that the past few weeks of smoking will be picked up by it, you might be wondering if there’s some way you can pass it anyway. Ideally, you’ll have long enough to stay sober and clean out your system. But the truth is that if you’ve been smoking daily or near-daily, it’s unlikely you’ll have long enough to pass it legitimately.

So what can you do? What are your options for passing a drug test when the odds seem against you?

The Main Ways to Pass a Drug Test

Your options are simple. Either you can abstain long enough for the specific type of test you’re likely to have, or you can combine abstaining as long as possible with a risky attempt to fool the test.

Urine Test

You’re most likely to be urine tested. In this case, if you use weed regularly, you’ll need two to three weeks to be clear, but possibly longer. If you don’t have time, you might be able to “wash yourself out” just before the test.

Saliva or Blood Test

If you’re saliva or blood tested, you’ll only need to be sober for a few days at most. Saliva tests can be fooled with some excessive mouth-cleaning, if you’re lucky.

Hair Test

This is less likely, but if your hair is tested you won’t be able to hide previous use. Instead, you can just wash your hair and hope that the screening doesn’t flag your use, which happens more than you may think.  

Each case is likely in different situations, and it’s useful to know the basics about the test and what exactly the criteria are for a “pass.”

Urine Tests Are the Most Common, Saliva and Blood Are Possible

Most drug testing in U.S. workplaces is in the form of urine tests, but it is possible you’ll be tested by saliva or blood. Hair testing is mainly used in rehabs or research settings.

In all of these cases, the first test is a “screening” test, where they essentially set a slightly higher bar to rule out false positives. However, if you’re looking to “pass” a drug test, this is really all you need to pass.

The table below summarizes the different cutoff levels for each test and what they’re looking for. The cutoffs for urine and saliva are set in the Federal Register, with blood and hair having norms based on state laws and common testing standards. Note that the targeted chemicals and cutoffs here are only for the screening test.

Type of testChemical targeted (Screening)Cutoff (Screening)
Urine11-nor-9-carboxy-THC (THCCOOH)50 ng/mL
SalivaTHC4 ng/mL
HairTHC1 pg/mg

You Might Pass Honestly Within a Couple of Weeks

The best way to pass a drug test is to avoid using substances on the lead-up to the test. For other drugs, this would only mean a few days of abstinence, but for cannabis, you’ll need at least two weeks to stand a good chance of passing.

RELATED: How Long Does Marijuana Stay in Your System?

The big problem for cannabis users is that weed stays in your pee for quite a long time, and that’s by far the most common method of drug testing. Evidence suggests that daily users can easily test positive for up to three weeks after their last use, and it’s possible that it could be even longer than this. However, it’s also possible that it could be less than this, so you might be able to genuinely pass if you have a couple of weeks.

However, it wouldn’t be much of a drug test if it was announced long enough in advance to clear your system of everything anyway. So it’s likely that you may need to take further steps, with the most common being taking steps to dilute your urine.

We spoke to drug testing consultant Joe Reilly, who said that in addition to diluting the sample, “Some of the tricks include products to drink, pills to take, adding substances to their urine, bringing in fake urine, and bringing in other people’s urine.”

Diluting Your Urine to Pass a Drug Test

Drinking lots of water for a couple of hours before the test is one of the simplest but most effective ways to try to pass a urine test when you probably wouldn’t. 

Dale Gieringer, PhD, a published researcher on the topic of cannabis urinalysis and director of California NORML, told us that, “Flushing with water and/or diuretics may be as effective as any of the detox kits on the market.”

In a blog post on the topic, he explains that provided you don’t give your first urine of the morning, drink plenty of water and take about 50 to 100 mg of vitamin B2 (for your pee’s color), you can fool the test. It’s hard to estimate exactly how much to drink, but it should be enough so that you pee once or twice prior to the test and can still go again when it comes to the test. 

Joe Reilly was a little more skeptical about the effectiveness of these approaches:

“The laboratory will do specimen validity testing and determine a dilute specimen where they cannot support a scientifically valid positive or negative result. Sometimes the lab can provide a negative or positive result even when the specimen is somewhat dilute. There are many variables involved with flushing out the THC metabolite so it is not a definitive answer as to ‘can this be a way to cheat the test or not?’”

Even though it’s far from perfect, it’s one of the best options because it is your own urine sample and unless the lab corrects for it, it will definitely reduce the concentration of THCCOOH.

Note that for your own safety, you should try not to drink too much water, especially if you know you have electrolyte, heart or kidney problems. It is not recommended to drink more than one gallon (4.5 L) of water daily to avoid hyponatremia and other electrolyte imbalance complications that can be serious and even life-threatening. This is rare, but can be experienced by marathon runners and other extreme athletes.

Other Methods Are Less Reliable, But Switching the Urine Can Work

Switching your urine for a friend’s clean urine or synthetic urine is difficult, but if you get by the person collecting the specimen, it can be effective.

Dale Gieringer also commented that “Urine substitution is the most popular and effective way of cheating on drug tests.”

However, Joe Reilly, the drug test consultant, points out that “Specimen collectors take their job seriously, looking out for signs of adulteration or substitution including checking specimen temperature, observations, and checking smell and color of the urine. Certified laboratories do specimen validity testing to determine substitution or adulteration.”

But you can keep these things in mind if you’re trying to trick the test. For example, people often place an IV bag of clean or synthetic urine attached to their inner thigh. This will keep the bag at body temperature, and if it’s rigged up properly, would be hard to notice dispensing urine unless the collector literally watches you pee.

Unfortunately though, and as Joe pointed out, both the collector and the lab are trying to catch these tricks, so really you’d be taking a risk by attempting it.

Tricking a Saliva Test By Clearing Your Mouth

The initial screening saliva test only looks for THC, so it’s possible to wash out your mouth thoroughly enough that you will pass the test.

Since a saliva test is basically detecting the THC deposited by the smoke or edible, it’s possible to clear this out before the test. 

We asked medical cannabis coach and CBD Oracle’s Medical Advisor Dr. Abraham Benavides about whether saliva tests would be able to detect edibles use as well as smoking:

“Edibles will produce less active THC in your mouth because the THC is a distillate dissolved into the product which is immediately ingested. Unless the edible is sitting in your mouth for several minutes like a tincture does, little THC is absorbed through the mouth or left behind except for the remaining food particles that can be washed out.”

This makes it technically possible (but certainly not a guarantee) that you could trick a saliva test by thoroughly cleaning your mouth. Dr. Benavides continues:

“While there is currently no data on deliberately washing out THC, it is possible that eating fatty foods and cleaning out the mouth may be able to expunge the THC ingested if it was dosed more than 2-4 hours ago. However, THCCOOH is still being produced and slowly excreted by the body long after the THC is gone. 

If you are a frequent consumer, washing out the mouth may help with passing the initial THC screening but if it is still flagged at and checked for THCCOOH then the detection window widens to a 2-3 day range minimum.”

He adds that “There aren’t any proven methods for passing a saliva test on short notice yet,” but suggests that the “Best bet is to abstain right away for 2-4 hours, drink a decent amount of water (at least 1L), and clean your mouth with tooth brushing and mouthwash to remove food particles.” 

Again, this is far from guaranteed, but it’s unlikely there will be a sign you’ve attempted to trick the test either.

Hair Tests Are Hard to Fool, But You Might Not Need To

For a hair test, you won’t be able to abstain for long enough, but you can just hope you’ll pass the screening.

Hair testing can reveal cannabis in the system for up to 90 days. However, it’s also true that controlled experiments find that only around 65% of regular users test positive. So while you likely can’t hide from the 90-day window, you may not have to.

Conclusion: Honesty Is Best… But You Have Options

We don’t want to encourage you to do something that is dishonest and could get you in trouble. However, if you’re using cannabis medically, in a legal state or just anyway, and you wouldn’t do it while you’re working, we don’t believe you’re a danger in the workplace. If you have a job interview coming up or need to keep your current position, it’s pretty hard to say you shouldn’t do what you can to protect your own interests against this outdated, useless and frankly degrading practice.

Additional Resources

View All References (8)

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  • Desrosiers, N. A., Himes, S. K., Scheidweiler, K. B., Concheiro-Guisan, M., Gorelick, D. A., & Huestis, M. A. (2014). Phase I and II cannabinoid disposition in blood and plasma of occasional and frequent smokers following controlled smoked cannabis. Clinical Chemistry, 60(4), 631–643. 
  • Gryczynski, J., Schwartz, R. P., Mitchell, S. G., O’Grady, K. E., & Ondersma, S. J. (2014). Hair drug testing results and self-reported drug use among primary care patients with moderate-risk illicit drug use. Drug and Alcohol Dependence, 141, 44–50. 
  • Huestis, M. A., Gustafson, R. A., Moolchan, E. T., Barnes, A., Bourland, J. A., Sweeney, S. A., Hayes, E. F., Carpenter, P. M., & Smith, M. L. (2007). Cannabinoid concentrations in hair from documented cannabis users. Forensic Science International, 169(2-3), 129–136. 
  • Kulig, K. (2016). Interpretation of workplace tests for cannabinoids. Journal of Medical Toxicology, 13(1), 106–110. 
  • Mandatory Guidelines for Federal Workplace Drug Testing Programs, 82 Fed. Reg. 7920 (January 23, 2017) 
  • Newmeyer, M. N., Swortwood, M. J., Barnes, A. J., Abulseoud, O. A., Scheidweiler, K. B., & Huestis, M. A. (2016). Free and glucuronide whole blood cannabinoids’ pharmacokinetics after controlled smoked, vaporized, and oral cannabis administration in frequent and occasional cannabis users: Identification of recent cannabis intake. Clinical Chemistry, 62(12), 1579–1592. 
  • Newmeyer, M. N., Swortwood, M. J., Andersson, M., Abulseoud, O. A., Scheidweiler, K. B., & Huestis, M. A. (2017). Cannabis edibles: Blood and oral fluid cannabinoid pharmacokinetics and evaluation of oral fluid screening devices for predicting Δ9-tetrahydrocannabinol in blood and oral fluid following cannabis Brownie Administration. Clinical Chemistry, 63(3), 647–662.