Urine Drug Testing and You: Marijuana Edition

How long does it take to have a negative drug test after using marijuana? 

Marijuana is now medically legal in a majority of states, but it still faces pretty intense scrutiny from employers. Until we get federal action preventing drug screenings, marijuana patients may have to weigh their use of marijuana with the potential of a new job. Should we try to fool the drug tests? Dr. Lee weighs in. 

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Dr. Lee

This is a question I get pretty frequently, and with good reason. Marijuana is now medically legal in a majority of states, but it still faces pretty intense scrutiny from employers. Until we get federal action preventing drug screenings, we as marijuana patients are probably going to have to deal with periods of abstinence prior to new jobs. That’s just the way it goes! 

Cue the anguished sobs of sober people searching for jobs. 

The primary psychoactive compound in marijuana, THC, is what causes the ‘high’ that marijuana users are accustomed to. Your body breaks down THC into a molecule called THC-COOH (also called carboxy-THC), which is then excreted in the urine. That’s the molecule that is detected in drug screenings. If your urine contains carboxy-THC above a certain threshold, your urine drug screen is considered positive, and you can probably kiss that job goodbye.

How long does it take to produce a negative urine drug test after consuming marijuana? 

The short answer is, it depends on how much you smoke, and how often you smoke. This is a table taken from the Mayo Clinic laboratory’s website (1). LOQ stands for “limit of quantitation,” meaning that it is the lowest concentration that can be reliably detected in the urine. While the LOQ here is 3 ng/mL, each lab has a different limit that it reports as a positive. For the Dept. of Transportation, the standard cutoff is 50 nanograms/milliliter (ng/ml).

Detection Times of Marijuana in Urine Drug Tests
Detection times vary depending on the frequency and quantity of marijuana use.

I think the real news here is that single-use and moderate use is relatively quickly passed through the body. Many patients assume that 30 days is the minimum for any kind of marijuana exposure, but for patients that don’t regularly use marijuana, it takes only 3 days for marijuana metabolites to clear. 

“I think the real news here is that single-use and moderate use is quickly passed through the body”

If you smoke every day, or a few times a day, you probably have urinary carboxy-THC levels greater than 500 ng/mL. You can expect this to take 30 to even 60 days to clear! Per the Mayo Clinic’s website, “Chronic use causes accumulation of THC and THC-COOH in adipose tissue such that it is excreted into the urine for as long as 30 to 60 days from the time chronic use is halted.”


Can I fool a drug test?

Probably not. 

There is plenty of hearsay on vitamin C, niacin, vinegar or various herbal ingredients might help you pass a drug test. There are also a lot of over-the-counter kits that proclaim that they will help you pass a test. I don’t believe in any of these, personally. Plenty of people hydrate copiously and exercise as well, but there’s no high-quality evidence that this has any effect.

In general, the only thing that has been shown to have any reasonable effect on a urine sample is to drink plenty of water to dilute the concentration of metabolites in your urine. According to NORML’s website, “While you’re loading up on water before the test, you may also want to take a large dose (50-100 milligrams) of vitamin B-12, available in B-complex multivitamins. The purpose of this is to color your urine yellow, since otherwise you are likely to produce clear, watery urine, which makes some collectors suspicious (contrary to rumor, vitamin C won’t help). In rare instances, some labs will reject a sample for being too watery; in this case, however, they will typically give you a second chance.”

Lasix, a diuretic, and high-dose aspirin have been shown to interfere with drug testing. But that’s kind of desperate and weird, and you should probably just stop smoking for a few weeks instead. 

If you are worried that you or someone you know is suffering from marijuana abuse disorder, check out this article to learn more about the signs of dependency.


Is there some way to alter my sample to pass a drug test?

Yeah…don’t do it. You’ll probably be nervous, you’ll probably get caught, and in my opinion, tampering with a drug test is so much worse than just testing positive from an employer’s perspective. The following excerpt is taken from NORML’s website, (2)

“Another trick to foil the test is to spike the sample with an adulterant. This approach should be used only as a last resort since any adulterant can be chemically detected if labs take the trouble to do so. A number of adulterants cause negatives on the commonly used EMIT test, but not necessarily other tests. In an emergency, you might fool an EMIT test by adding a few drops of Visine® to the sample. Other common adulterants include detergent, bleach, salt, and the cleaning solution glutaraldehyde, but most of these are easily detected by smell or visual inspection. 

A host of commercial adulterants are on the market (for advertisements, see High Times). Among the more popular are Klear® and Whizzies®. No additive is 100% reliable, and all involve a substantial risk of detection. Many drug testing companies claim to test for adulterants, though it isn’t clear how carefully.”


Why Drug Testing Is Pointless

Urine testing has actually never been scientifically proven to be an effective way to improve the workplace. According to several studies launched undertaken during the ‘War on Drugs’ when drug testing had a popularity boom, employees testing positive for drug use are just as reliable as others and the tests themselves aren’t reliable at determining drug impairment. (3, 4)

As far as marijuana goes, a lot of people  (reasonably, I think) wonder why employers test for its use at all. Does using cannabis outside of work hours really impact your performance or workplace safety? Americans were recently forced to grapple with this idea when Sha’Carri Richardson was banned from the Tokyo Olympics for testing positive for marijuana.

Sha'Carri Richardson crosses finish line during the Tokyo Olympic Trials

A lot of Americans watching this play out in the news cycle were skeptical that marijuana use would somehow enhance an athlete’s performance in a 100-meter sprint. And while most of us won’t be entering the Olympics anytime soon, it did highlight the absurdity of drug testing for marijuana and its relevance to have a successful career in a variety of fields.

Without diving into the history of the ‘War on Drugs’ and its impact on the Black and brown people of our country, let’s just say there are a myriad of economic, political, and social interests (including racism) at play here.  No matter its nefarious origins, until something changes at the Federal level many marijuana patients will come face to face with a mandated drug test.

A Little Philosophy 

The only reliable way to pass a drug test? It’s actually to stop using drugs. This is kind of your come-to-God moment. If you’re really incapable of stopping your marijuana use for a brief period, and it compromises your employment, you’re creeping into marijuana-abuse-disorder territory. I am as big of an advocate for marijuana as there is, and one of the things that I emphasize is each person’s relationship with the herb. Becoming overly dependent on anything is not dope. Being unable to stop marijuana use for a few weeks is not dope. 

That’s my edict for your average recreational user or healthy medical user that can get by utilizing non-marijuana treatments for a while. I truly do believe that there are patients out there suffering from severe, hard-hitting medical diseases for whom marijuana is the best or only reasonable treatment. It is these people that we are really harming with medical drug testing. 

I, personally, am not one of these people, which is why I’m sitting on my ass sober for six months. WOMP WOMP. Light one up for ol’ Dr. Lee if you’re reading this!


Dr. Lee’s Tips for Passing a Drug Test

Finally, this is the moment you have been waiting for. I have two tips for anyone hoping to pass a drug test in the ‘iffy’ range- the range where you might be negative, but might still be close enough to marijuana use to be positive. 

  1. First of all, avoid giving a sample from your first urination of the day- metabolites are known to concentrate in the urine during sleep.
  2. Second, get a drug test from Amazon or a head shop and test yourself- it’s the only way to have any confidence about your results without guessing.

All of our patients at Green Mind get lifetime marijuana support from our doctors. If you would like to discuss drug testing with one of our physicians, simply book a free follow-up appointment.


  1. “Drug Testing: Marijuana- Mayo Clinic” https://www.mayocliniclabs.com/test-info/drug-book/marijuana.html
  2. “Drug Testing – Marijuana Testing Tips” https://norml.org/marijuana/drug-testing-tips
  3. John Horgan, “Test Negative,” Scientific American, March 1990; Dr. John Morgan, “Impaired Statistics and the Unimpaired Worker,” The Drug Policy Letter, May/June 1989.
  4. Consensus Report, National Institute on Drug Abuse, Journal of the American Medical Association, Nov. 8, 198