Your quick guide to the urine drug testing for cannabis use and what strategies work to beat the tests.

In most cases, urine drug testing for cannabis is an invasion of privacy and a giant waste of resources. However, until drug war hysteria is a thing of the past, it is a reality that we will need to deal with.

Unfortunately, the amount of misinformation on the internet about drug testing is astounding. My unscientific estimate is that 85% of what you read about drug tests and how to beat them is utter bullshitMany people writing about drug testing are, at best, well-intentioned but with no clue, and at worst, purposely misleading you for commercial gain.

This article will provide you with

  • A basic understanding of urine drug testing for cannabis
  • Strategies to beat drug tests that work and those that are just myths

[Always test yourself to know whether you’ll pass! Here are the test strips I recommend.]


Urine Drug Testing for Cannabis Use

Let’s start with an infographic to give a quick overview:


Specimen Validity Testing

After collection of the urine sample, the first thing a lab will do is check whether it is a valid urine specimen. They want to make sure you didn’t substitute the urine for something else or add anything to it. They may check the following:

  • Color and appearance: Urine should have normal color and not be cloudy.
  • Temperature: Urine should be within normal body temperature range.
  • Creatinine: This is a by-product of protein metabolism. Low levels of creatinine may indicate that specimen is not real urine or that it has been diluted.
  • Specific gravity: This tests the density of urine. Similar to creatinine, it ensures that specimen has not been overly diluted.
  • pH: Urine should be within normal pH range, as extremes of pH will interfere with the drug tests.
  • Adulterants: Adulterants are any substance added to the urine to cause a false negative on the drug test. Many oxidizing agents (e.g. bleach) will do this. Common adulterants are now tested for by many labs, although what specifically they test for may vary.

Types of Tests for Cannabis Use

Urine drug tests for cannabis use do not test for THC itself since little THC is actually excreted into the urine. Rather, they test for metabolites of THC, which stay at detectable levels for much longer (It may help to be familiar with the basics of THC metabolism).

There are two types of tests that can assess cannabis use:

  • Immunoassay test
  • GC-MS test

The immunoassay test is used as a rapid and cheap screening test. This is the same type of test that is used in point-of-care home drug testing kits.

So why don’t drug testing companies just use the immunoassay test by itself? The problem is that it produces a high rate of false positives  – it gives a positive result for cannabis use even when you have not ingested any cannabis.

The drug testing companies are obligated to use GC-MS as a confirmatory test to ensure you have actually used cannabis. The confirmatory GC-MS test is extremely specific – it produces almost no false positives.

So why don’t drug testing companies just use the GC-MS test? It uses expensive equipment and is much more time consuming. Companies would either need to charge more for drug testing or accept a much lower profit margin.

One proposal has been to spike all urine samples with something that will cause a false positive on the immunoassay (while still passing the GC-MS). Drug testing companies would be forced to spend a lot more money on confirmatory tests. Eventually they would have to raise prices, reducing adoption of unnecessary drug testing!

[Always test yourself to know whether you’ll pass! Here are the test strips I recommend.]


Beating Cannabis Drug Tests

What actually works for beating drug tests and what doesn’t? Much of the information out there is wrong. Drug testing myths get endlessly repeated.

I will cover every strategy for beating cannabis drug tests and evaluate whether there is any evidence that it actually works. Each article will have an in-depth scientific explanation, so you know that it is for real.

Come back regularly, sign up for the mailing list, or follow me on Twitter/Facebook to see when there is a new update!

Strategies That Don’t Work

Strategies That Do Work

[Always test yourself to know whether you’ll pass! Here are the test strips I recommend.]

Last modified: February 14, 2018

68 Responses to " Guide to Urine Drug Testing for Cannabis "

  1. Charles says:

    Can a test become lessened while waiting to be sent to the lab if only trace amounts are present

    • Prof of Pot says:

      They will probably store the sample at a temperature that the metabolites are stable. But if only trace amounts are present, then you will be below the cutoff anyways.

  2. Mary Jane says:

    Iam subject to urine analysis whenever the company feels fit, I currently read that CBD does not give you a false positive for marijuana. I ordered a vaping oil that indicates there is no THC, however he product said it contains traces of THCV. Will THCV test positive on a urine analysis test?

  3. Linda says:

    If I have a prescription for medical cannabis ( not from my primary care doctor)can he test me with out my permission ? I take medication for depression ( from a psychiatrist) and my primary gives me a hard time about taking these medications, every time I see him? I am in good health, and exercise every day, just can’t sleep with out a couple of hits off my pipe! If I have a cannabis medical card, why is my Primary Doctor giving me such a hard time?It does not affect my health

    • Prof of Pot says:

      A primary care physician cannot force you to take a drug test (or any test for that matter) without your consent. Although I have heard cases where they refuse to prescribe opioids without passing a drug test for THC. I can’t say why your physician has that attitude, but you could always search for a different one.

  4. Kurt says:

    Tested myself for marijuana on day 32 clean … day 35 positive… days 37 and 38 neg … today day 40 tested myself twice both positive! Ugh I’m left no choice but to use synthetic here in California. This is for a pre employment screen? What to do here?

  5. Mickey says:

    If your being drug tested for weed is there any way they’ll find anything else?

  6. Jason says:

    I was wondering how fast two hits off of a pipe might last and nick me on a drug test. I am a truck driver and I know that the test for truck drivers are a bit more strict. My brother came over yesterday and I took one hit off of his pipe and was good with that. Then about 3 hrs later I took another. I haven’t smoked for over two years prior to that and I woke up this morning to a text message from my boss telling me that I had to do a drug test within the next 10 days. Is there even enough thc to show up in a drug test if it’s only been a couple tokes?

    • Prof of Pot says:

      If it’s enough for you to feel high, then it’s enough for you to fail a drug test. However, it will leave your system quickly, since there won’t be any accumulation from multiple times. Smoking a single time usually doesn’t cause a positive for more than a few days.

  7. Nate says:

    Is there any type of creatinine that can be added to your sample. If there are stories of people using synthetic urine and passing, how does it pass the validity screening if it is not human. I also did not find anything you have written on synthetic substitutes. Or did I overlook it. Your reaseach and explanations are amazing and a breath of fresh air please keep it up!

    • Prof of Pot says:

      You could in theory add creatinine and salt (for specific gravity) directly to the urine sample. I’m not sure where you can buy creatinine, but surely it must be available somewhere on the internet. At that point, you might as well consider synthetic urine or a clean sample. I assume the synthetic urine already has creatinine and everything else needed to pass in it.

      I have not written about synthetic urine. Not because I don’t think it’s a valid technique, but just because I don’t have much else to add on it beyond what others have written. Synthetic urine has its own challenges, especially if the collection is being observed, so it’s not for everybody.

  8. Aija says:

    Hey prof! I’m freaking out and have a question.. so I was a heavy smoker of marijuana for about 2 years stopped for 4 months got a job and passed the urinalysis. However, I started again and stopped for 70 days… lol then I started smoking for 5 days (1 blunt a day) and found out I have a urine test in 11 days. I heard that cranberry pills work really well and was going to get some at home tests. I’m female 5’5 and 155 pounds!

  9. Emery says:

    Hello, I’m going to start using charcoal and eating high amounts of fiber as you suggested in your articles. I’ve been a daily user of cannabis oil to help with my hypomania, and if I can break the cycle of reabsorption in the intestines (which I didn’t know happened), I will definitely take advantage. Maybe that’s part of why detox takes long?

    My main question here is about things like “Certo” and “Sure-Jell”. I hear they have a similar effect the charcoal has–picking up more in the intestines so less will be in the urine. Is this a myth? Should I add this to my detox regimen? Finally, is there any additional advice you have for Me? I was just accepted to nursing school the 11th of October. I’ve been clean for about a month. Vitamins, clean eating, take vyvanse everyday, exercise 2 hours daily, use heat therapy (sauna) to increase cardiac output and glomerular filtration rate in kidneys (assuming it has an effect on the rate of THC metabolite excretion), and drink tons of water–that’s what I’ve been doing so far. My drug test is in a week. Thank you so much for your time, and for writing these helpful myth-busting articles.

  10. Ryan says:

    I was using synthetic urine in the testing facility. After pouring the urine in cup, I went to pee in the toilet to fool the facility. Upon peeing in the toilet, a little got into the sample. Will that make my test positive?

    • Prof of Pot says:

      It’s not impossible that it would cause a positive, although it would be very unlikely. It depends on what your levels were and how much got into the cup. If a typical urine collection is 30 mL and you got let’s say 2 mL in the cup, then it’s a 15-fold dilution. You would have to have some of the highest urine levels I’ve ever seen to have this cause a positive.

  11. Tom Jones says:

    I’ve been taking the home tests the you recommended the past 5 days. The clarity of the lines has been improving and passing clearly and consistently at 50ng and been getting somewhat faint but decent lines at 20ng today. I’m taking a urine test tomorrow. I’m afraid to trust the strips and have a synthetic, but I’d prefer not to use it. How much should I trust the at home strips? Thanks prof.

    • Prof of Pot says:

      Good question, but I can’t answer it without seeing the validation tests that the companies ran, which as far as I know aren’t publicly available. I would assume that they’re reasonably accurate, within +/- 15%. Having a little buffer room would be a good idea, even just considering that your urine will be a little different every time.

  12. Mady says:

    Thank you for the information! I have been a daily smoker for over a year, some days I’d smoke less than a gram, other days more. I am 21 years old, 5 feet tall and 115 pounds. I have a fairly high metabolism, I work out a couple times a week, I also have a job that I’m on my feet the whole time. I stopped smoking September 10 because I know that I’ll have to take a drug test in December or January, so I wanted to give myself plenty of time to naturally detox. However I am becoming more and more worried as I read forums online that it’s taken people 90+ days to detox since they were heavy smokers. I am not worried about passing the 50ng cutoff level, but I take a prescription RX (benzodiazepine) that I know will show up during the initial that will cause it to go to the GC/MS which has a cutoff for 15ng. My question would be do you think I will have naturally detoxed all of the THC out by then or should I start considering subbing or dilution method? Thank you so much!

    • Prof of Pot says:

      You will probably be fine. I would still dilute your urine and test yourself with this method:

      • Mady says:

        Just to be confirm, if I dilute will they not be able to pick it apart during the GC/MS? Or since it is going to further testing will they be able to tell regardless? I have ordered the activated charcoal and will start that on Friday, I also ordered a pack of 10 drug tests from amazon to test after 30 days.

        • Prof of Pot says:

          They try to find out if you diluted a lot by measuring creatinine and specific gravity. All the details of how to dilute as much as possible without going over the line are in the link. I recommend doing at least one test run beforehand.

        • Mady says:

          Thank you so much for clearing things up for me! I ordered a box of tests, wanting to test on day 30 however when I received them I tested myself on day 18 and shockingly enough I PASSED! I was surprised and wanted to make sure it wasn’t faulty so I tested my boyfriend (daily smoker) and he failed. I’m going to keep taking the activated charcoal twice a week but I’m so glad I came across the information you gave. Thanks again!!

  13. Nick says:

    Prof please help I’m going nuts and I’m a heavy user what should I do to lower my the levels prof and comments would be great

  14. Nick says:

    I there I smoked today but I have a test Monday they said that my levels need to be lower than the last test it was last Thursday it’s a po test would activated charcoal help if I did it for the next 3 days cuz I really want my levels to go down I plan on not smoke anymore till I get off please Lmk if I should get some to help me out

  15. A. says:

    Hello Prof-

    I was a heavy user but stopped completely and tested preliminary positive on 3 different home tests over days 33 and 34 of abstinence. I weigh 195 lbs, exercise 4 days a week and drink several quarts of water a day. I would guess my BMI is around 15-18 (I’m stocky but not fat). One week until my pre-job urine test.

    Do you have preferred brand of activated charcoal?
    Could my ketogenic/high-fat diet be a problem?
    Are there any strategies you would suggest?

    I’m freaking out and any help would greatly be appreciated. Thanks.

    • Prof of Pot says:

      I’ve been meaning for months to recommend a brand of activated charcoal, but unfortunately I haven’t had time to research it. People seem to like the powder ones instead of the capsule ones because they can take larger doses. I don’t think your diet will necessarily be a problem, except that if it doesn’t contain any fiber, you may have missed some opportunity. Fiber somewhat acts like activated charcoal, although it is weaker. At this point, just go straight to the activated charcoal. I would continue to exercise, cutting as much fat as possible in the next week. On the day of the test, drink plenty of fluids to dilute the urine.

  16. Jusswavy says:

    My drug test came back positive as the same metabolite level before which is 47 so I’m starting to put two an two together am I being sabotaged? Because they is no real reason why my metabolite level will stay the same after 70 plus days of not smoking weed! I really feel like they sabotaging my employment!

  17. Lou says:

    How long does THC stay in sir of a not so well ventilated room? Roomy is a pothead and I am afraid I will fail my test because of exposure. I’m 5’5 165 lbs ~25% body fat and female. I’ve abstained 72 days but still coming up positive on home tests. Do you think it’s cause of the roommate?

    • Prof of Pot says:

      I would be pretty surprised if you failed due to second hand smoke (unless we’re talking hotbox level of second hand smoke). But also 72 days should be more than enough time to clear your system. You could try avoiding the smoke for 5 days and retesting yourself. If this doesn’t produce a positive, then I suspect that the home test is giving you a false positive.

      • Lou says:

        Thanks!! I did 2 days of the activated charcoal to be safe at 5g/day and FINALLY I’m getting a negative home test. I’ve got a test at end of week. You suggest 2 days on charcoal and 5 days off. Do I have to wait or can I squeeze in another day of charcoal? (Yes I’m over panicked, must pass…) Thanks for the advice!

        • Prof of Pot says:

          2 days on and 5 days off is just a suggestion…it is not set in stone. You can always take more, but the longer you take it, the more you risk some uncomfortable side effects such as constipation. I think if you are that desperate to pass, it could be worth it.

        • Lou says:

          Thanks! I appreciate fast response.

  18. Mike says:

    I go to a day report center and get drug tested frequently. My last drug test for THC got me a two week shocker in jail. I have not smoked and am a male 6’4″ 410 lbs and have not smoked pot none whatsoever. I missed the 4th of July with my family and crushed me. I should have been cooking out and letting fireworks off with my son. I urinated once and didn’t meet the mark so I had to use the same cup again and I believe that is what caused the spike due to clean catch protocol not being followed. I don’t know the specifics but what do you all think? Thanks for any replies.

    • Prof of Pot says:

      Hi Mike, I’m really sorry that happened to you on your 4th of July. Such a shame that our justice system thinks it is more important for you to be in jail than to be with your family. It is impossible to say for sure why you didn’t pass the test. I looked at the clean catch protocol ( and there is not any evidence that this is a factor. It does sound like you were dehydrated though, which can concentrate THC metabolites. Next time, I would drink plenty of fluids in the hour before the test to dilute your urine.

  19. JohnnyD says:

    So let me get this straight – if I don’t become a subscriber, you don’t publish my comments? Is that how this works? Because if it is, you can fuck off and earn your money off of someone else.

    • Prof of Pot says:

      Nope, I just have to approve comments before they post, something that I only have time to do once a day. I haven’t earned any money off of you or anyone else from this site.

  20. JohnnyD says:

    Recently urine tested for employment after staying entirely clean of weed for 30 days. The test was one of the color-change types, similar to a pool or spa water test strip.To my surprise, the result came up positive not for weed, but for adulterants of some sort. They put it as “No clear result for marijuana”. Trouble is, I never used any adulterants, ever. Any idea how this could happen? They sent the sample off to a lab for further testing, which I hope will give a better result, but the ambiguity may have already cost me the job.

  21. Jusswavy says:

    The only details they gave me was that my metabolites were low, it’s crazy because I used to be a moderate smoker of weed an the fact I weigh less than 110 with 40 plus days of being sober it’s like I’m all out of theories of what could it be because I know it ain’t the cigarettes or other tobacco related products. Since then I’ve been taking detox products like 3 days cleanse an anything cranberry related products, sweated a lot, drinked water and a occasional soda .. I virtually have little body fat on me I’m lean with some muscle 🤷🏾‍♂️.. am I being sabotaged I’m all out of theories and money 🤦🏾‍♂️ it’s very odd how folks who weigh more than I do pass these drug tests so easily I’m skinny for Christ sake 😂

  22. Jusswavy says:

    I weigh 105 barely workout an it’s been 40 plus days of being sober an still tested positive!! Any advice doc? Btw my metabolites were low so what he hell gives!!

    • Prof of Pot says:

      40 days is a really long time, but this has been seen before in heavy users. What type of test did you take? I’m a little confused, because if your THC metabolites are low, then you should pass. Can you explain further?

      • Jusswavy says:

        It was a urine analysis test but I also was drinking a lot of water days before so could it possible that they decided to fail it because of the amount of water I drinked that made it look like I was trying cover it up!??

  23. Glen James says:

    Following up from my previous comment – just passed at On Home test on Day 6. Feeling a million times better now 🙂

  24. Glen James says:

    Amazing site providing truly quality resources…. thank you!! I’ll keep this short and sweet – male, 31, 5’9″, 165lbs, sz 32 waist, probably 15%ish body fat. I smoke 3/4 times a week. Taking pre-employment drug test on what will be my 10th day clean. Odds of passing? Suggestions to help??

    Eternally grateful for your time and the information you’re providing. On my way to the store to get a bottle of activated charcoal right now.

  25. Heisenberg says:

    Thank you profofpot!

    i’m worried i will fail my drug test. i smoked 4 times last month and i have a drug test that is needed within june 12-16 for my internship and since then i’m gaining some pounds. will i pass it?

    p.s. my last session was in may 25.

  26. Fred says:

    P.S. I passed at 49 days, however, went heavy on hydration pre-test and came out diluted…Ooops…was self testing prior with home strips showing faint line negative… The. First results scared me being a straight out “lab” test with SVT applied!!

    All good and happy to be in spot I am..

    Thanks again Doc…. I did do a few rounds of charcoal…

  27. quinten says:

    i am 163 pounds also

  28. quinten says:

    i have a drug test in 8 days and ive only smoked 2 times last week and 1 time the week before and about 2 times the week before that week and i think once again the week before THAT week also.. alot of week i know… what can i do now since ive stop smoking since saturday to flush out of mask the thc that may still be in my body, on sunday i was doing cardio for 40 min sweating alot and went into the sauna for 20 minutes,, (im not an everyday user, i smoke sometimes or less) and then on monday went for another run in my neighborhood, and since sunday ive been drinking 8 small cups of water a day? will i be ok by the time june 8th rolls in?

  29. Fred says:

    Thank you for your info. In short, I have been a heavy user of high quality flower. I have had urine tested in the past and was clear at 30 days, albeit lower quality of bud.

    My last test (as mentioned above) my body weight was 190 lbs. I current weigh 150 lbs….Yes I have lost body

    Currently I have a scheduled pre employment urine due in 16 days.

    I’m 31 days abstinent and show positive with home test. To say the least I’m a tad worried….

    Note: the home testing has been with little hyperhydration and no morning voids…

    Any advise would be greatly appreciated.

    P.S. I do have one option of push test forward by 7 days but would like that as last resort…oh, thought I had great DNA, maybe not for this instance.

    • 16 days is still a lot of time. It would be very rare to test positive after 47 days of abstinence, especially at lower body fat (good job on the weight loss by the way!) There can be a lot of variability in test results, with urine concentrations varying up to 3-fold even within the same day.

      Drinking enough fluids immediately prior to the test can make a big difference. I would continue using the home test strips every few days, but with drinking extra fluids in the hour before you test yourself.

      You can also use activated charcoal, which will help clear your system faster. There is solid evidence that this works, and I am writing up an article on it now that will have further details. Good luck!

      • Fred says:

        Thanks Prof,

        Ah, activated charcoal, brings me back to working in the ER days..

        Would zinc also be a worthy try?

        In addition, I have been consuming alkaline antioxidant H2O….not specifically for this issue but feel it may also assist with the “clean up”.. What is your opinion ?

        You have a great page and I plan to follow regardless of my current status.

        Thanks again for your valuable time and consideration.

        • Thanks for your support!

          Some people doubt activated charcoal works since they think that THC metabolites don’t go to the GI. However, due enterohepatic recirculation, the THC-COOH metabolite is constantly cycled in and out of the GI tract where it can be trapped by activated charcoal. This has already been proven by a pharmacokinetic study. I will provide more details on this soon.

          I haven’t researched zinc in depth yet, but from a quick search, it looks like it is worth trying. Taking the right dose is probably the key.

          Antioxidants shouldn’t make much difference since they won’t directly affect either THC metabolism or redistribution of THC & metabolites from fat.

          The alkalinization probably won’t matter much either. Almost no THC-COOH is directly excreted into the urine, which means that it is almost completely reabsorbed in the renal tubules. In theory, alkalinizing the urine could cause an ion trapping effect that would block this reabsorption and lead to more excreted in the urine. However, given the pKa of THC-COOH, it is probably not possible to achieve such low urine pH that significant ion trapping is achieved. Besides, there may also be active transport that would negate the effect of urinary alkalinization. Basically, it is theoretical and probably doesn’t do anything.

          There is one other strategy – to inhibit the enzymes responsible for glucuronidation of the THC-COOH metabolite. I am also working on a write-up for this, so stay tuned.

        • Fred says:

          Will do!

          I’m considering charcoal 1 week prior to test date.

          Will keep you posted if ok…


    • Sunshine Princess says:

      Great information Prof, thanks so much.

      Can anyone tell me if cannabis can affect the results of a standard urine test (for UTI)?
      Giving a false positive or negative result for Leukocytes (white cells) Blood, Ph, protein & Nitrites for example.

      Thanks guys