It has been widely reported that you should not exercise prior to a drug test for marijuana to avoid burning fat and releasing THC into your bloodstream. Is there any scientific evidence for this?

Today I will examine a claim surrounding exercise and drug testing: You shouldn’t exercise prior to a drug test for marijuana or you will burn fat and release THC that will cause you to fail the test.

Recommendations range from not exercising immediately before the test all the way to stopping exercise a week before the test.

Let’s examine the science behind this claim. But first, we need to understand some basic concepts of THC metabolism and drug testing.

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

THC Metabolism and Pharmacokinetics

You should first familiarize yourself with the basics of THC metabolism and how urine drug tests for marijuana work. Here is a quick summary though:

When you smoke marijuana (or consume via any other route), THC distributes from your blood into fatty tissues. If you are a regular marijuana user, the levels in your fat will build up over time, making it take longer to clear out of your system. The more fat you have, the larger will be your pool of fat-stored THC.


THC metabolism urine excretion basic


However, it is not THC that urine marijuana tests detect, but metabolites of THC. One of the major metabolites of THC is called THC-COOH. This metabolite also distributes to the fat to a large extent. THC-COOH is converted to the THC-COO-glucuronide metabolite, which is excreted into the urine.


Studies on Exercise and Drug Testing

Two scientific studies have looked at the effect of exercise on THC and metabolite levels. In fact, the first study has been widely cited as “proving” that you should not exercise immediately prior to a drug test.

Let’s see what conclusions the authors of the first study draw:

 “Overall, these results suggest that exercise may elevate blood THC levels by releasing dormant THC from fat stores.”

Sounds promising, but let’s see what the authors of the second study conclude:

“We conclude that exercise…is unlikely to cause sufficient cannabinoid concentration changes to hamper correct interpretations in drug testing programmes.”

So it looks like there is a possible conflict in the results of the two studies. I guess we’ll have to look at the details and draw our own conclusions.

In the first study, 14 regular marijuana users performed moderately-intensity exercised for 35 minutes. In the second study, 6 regular marijuana users performed moderate-intensity exercise for 45 minutes.

Investigators took blood samples prior to exercise, immediately after exercise, and (in the first study only) 2 hours after exercise. THC and THC-COOH levels were measured in the blood samples.

Effect of Exercise on Blood Levels of THC and THC-COOH 

In the first study, THC levels in the blood increased an average of 12% after exercise (although they returned back to baseline levels within 2 hours). In the second study, blood THC levels increased by an average of 25% after exercise. 

Given that a similar increase in blood THC levels was reported by two independent studies, I believe that this is real. However, does a small (and short-lived) increase in blood THC levels matter in the context of a urine drug test that measures metabolites of THC and not THC itself? 

Prior to exercise, study subject’s blood levels of THC-COOH were 25 times times higher than THC. THC does not get into the urine for the most part except through the THC-COOH pathway. If levels of THC-COOH do not change with exercise, what happens to THC levels is not that important.

So what happened to blood levels of THC-COOH after exercise? Neither study showed any change in blood levels of THC-COOH after exercise. The lack of change of blood THC-COOH indicates that exercise will not have any immediate effect on a urine drug test.


Effect of Exercise on Urine Levels of THC-COOH

The blood results are pretty convincing, but it is even better to look directly at THC metabolites in the urine after exercise. Although the first study did not collect urine, the second study did collect urine before and after exercise. As is typical in many drug testing labs, they converted all THC-COO-glucuronide to THC-COOH prior to testing.

Urine THC-COOH levels were on average 23% lower after exercise. Given the small number of subjects in the study, the decrease could be by chance, but it does not seem likely that exercise is going to increase urine THC-COOH.

Myth Busted?

We can consider this myth busted. If you are taking a typical urine drug test for marijuana, exercising right before the test will likely not have any effect on whether you pass.

Although it is true that exercise will cause a small increase in blood THC levels (which lasts less than 2 hours), this does not lead to an increase in THC metabolite levels in either the blood or urine.

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

[Featured image credit: Flickr/ Nathan Rupert]

Last modified: September 11, 2017

18 Responses to " Can Exercise Cause A Positive THC Drug Test? "

  1. John says:

    I havent smoked weed for 2 months and i was a heavy smoker i did a self urine test and saliva test and was both negative, i then did an hours intense swimmiming 2 days in a row which i havent done for years, that night i did a urine test and i was negative but the next day i did the saliva test and was shocked to see that it was possitive for thc, so yes excercise can make you prove possitive for drug test

    • Prof of Pot says:

      What kind of saliva test was it? Can you provide any details on brand, etc? I believe that most saliva tests measure THC, which is a bit different than the urine tests that measure THC metabolites. Studies have shown that THC levels go up after exercise, but I am surprised that they would go up enough to cause a positive in someone who hasn’t smoked in 2 months.

      • John says:

        It was mouth swab 7 drug salvia test, using salvia collector with sponge on the end, salvia tube and salvia test. the brand is home health uk

  2. melissa says:

    Unfortunately recent circumstances have proven that in people with a higher BMI THC levels actually did increase from week to week depending on the exercise. I have not ingested any cannabis since June 7th and have been getting tested weekly since. In the end of July the levels in my urine went from 20ng to 106ng and have been fluctuating ever since. I can say with absolute certainty that exercise has definitely caused the THC levels to change.

    • Prof of Pot says:

      I won’t say that it is impossible, just that under the circumstances of these studies, no increase was seen. In these studies, the subjects exercised just once and they looked for immediate increases in THC and metabolite levels. I get the impression that you are talking about a sustained exercise program over several weeks with weight loss?

  3. Jason khan says:

    Last night i got injury at work and was taken to hospital they fixed me and took me for drug test i was paranoid coz i quit smoking let say to be exact 1 month ago i used to smoke 2 blunts a day sometimes 1 or none not heavy smoker. When i was done from hospital at 7am i bought OC drug test and both test showed faint ghost line.

    Today morning i jogg/cardio(outdoors) for 1hr and again did drug test after waiting 1hr and guess what i failed slept for 4hrs again drug test failed.

    Do not exercises at least 2-3 days or 1 week prior to drug test thats my personal suggestion just to be on safe side.

    180lb 35yrs

  4. Chris Evans says:

    so does excersing to burn the fat cells help you pass or no??

    • Prof of Pot says:

      Yes, exercise will definitely help pass, but only if you do enough to actually change your percent body fat. That is actually the topic of a different article:

      I’m going to retitle this article because I realize its not very clear. This article is only covering whether exercising within a few hours before a drug test will put you at risk of failing. It’s a different question from whether you should exercise in the weeks leading up to a drug test.

  5. Angela says:

    Oh wow! This is the 1st forum I have found where it appears you have an extensive knowledge about THC & THC-COOH. Ok I’m 47 5’6″ 240lbs. I quit in January because I found out they were going to be testing us at work because they determined my job fell under DOT, therefore California laws don’t matter regarding pot. In May I failed the DOT test because I was over the 15ng limit. I have been going thru drug treatment program ever since. My test 5/17 208.5ng, 5/22 84.9ng, 6/6 100.6ng, 6/21 67.9ng, 6/28 59.1ng, 7/7 22.2 ng & 7/14 76.1ng??? Wtf? I have people telling me it’s in my fat cells and I have people telling me my home is covered in THC resin. I’ve also read about false positives and I do take Wellbutrin 150mg and I take approximately 12 aspirin per day, both came up on the list of things that cause false positives. I’m so terrified I’m going to loose my job and at a loss as to why I keep testing positive or how to stop it. Please please please at least give me some direction if you don’t have an answer.

    • Prof of Pot says:

      Hi Angela, I read your whole comment, but I hope you don’t mind I edited down a bit here. The aspirin and Wellbutrin won’t cause a false positive. I think in the past aspirin may have done this, but they have reconfigured the test so that it no longer does. I’m also a bit skeptical about the home being covered in THC resin causing an increase. THC is not very easily absorbed from the skin. There was a study on this recently and even fairly high amounts of THC applied without the proper formulation did not cause a positive on a drug test. Nonetheless, this is one of the longest times I have ever heard of someone being positive without smoking. Were you getting a lot of secondhand smoke from your husband?

      I am actually not surprised that the metabolite levels are jumping around. This is completely normal. There are studies where they had people in an in-patient unit (so they couldn’t possibly smoke) and they measured the urine metabolite levels every single time they went to the bathroom for like a week. Even within a single day, the levels could vary by 3 times or more. You probably do have a lot stored in your fat if you are still testing positive this much later. This means that you are losing it very slowly and the amount you lose in 1 week is not very large. The numbers do look like they are trending down overall between 5/17 and 7/14, but it is unfair of them to expect it to go down every single week. It will jump around a bit and some weeks it may go up without smoking.

      Have you been controlling how much fluids you drink before each test? This is a major factor. For example, you may have drank a lot more water on 7/7 than 7/14 without realizing it. This alone could explain the increase. If you want, I can send you a study that shows how much the test results can jump around. Maybe you can show this to the people in the drug treatment program.

  6. Chris says:

    So I can tell you from personal experience that I believe exercise does increase the risk of failing a urine test. Just this past year I was in a 3 month treatment center and prior to arriving I was a daily smoker. I was also overweight, weighing around 250 pounds. I was tested up to 3 times a week. The first month of tests showed decreasing levels of THC metabolites. 3 weeks into treatment I began doing high intensity interval workouts along with nightly jogging. I was able to pass a urine test after a month and it was at that point the treatment center considered me clean.

    2 weeks later I was pulled into the Dr’s office and completely caught off guard when they told me I failed a urine test for marijuana. I absolutely never touched or was even around any marijuana the entire time I was in treatment. I have 0 reasons to lie about this. I explained very sincerely how I did not touch any marijuana. They believed me and gave me another test 2 days later and it came back negative. The test that came back positive was also the only test where I was woken up at random in the middle of the night. It was a more concentrated urine sample. I am not sure if this effects the test or not, but what I do know is that I never smoked and marijuana. I poured over the internet trying to find an answer when I came across many others who said they had passed tests and been working out heavily and had been losing weight. I even checked all my medications to see if they had a possibility for a false positive and none of them did. The only logical explanation is that my high intensity workouts caused my urine sample to come back positive. I have spoken to 4 other rehab patients and they all had very similar stories.

    • Chris says:

      I meant to say, ” I came across many others who said they had passed, been losing weight, and then failed.”

    • Prof of Pot says:

      I’m going to test this scenario with the pharmacokinetic model as soon as I get a chance. I will report back once I get the results.

      • Prof of Pot says:

        In case you haven’t read it, you should take a look at this article: I think your situation is more along the lines of what I talk about in that article.

        I used a pharmacokinetic model to examine what the effects of rapid weight loss would be. I will need to write another article to show plots and explain the results properly. I’ll try to explain briefly here though:

        As you lose body fat, THC is pushed into the blood, more metabolite is formed, and more metabolite ends up in the urine. So there is a transient increase in levels for a few days, but the increase is predicted to be incredibly small (1-2%). However, there is a cumulative effect of these slightly increased levels of excretion and as you continue to lose body fat, the THC levels in your blood will start to drop faster than if you hadn’t lost weight.

        Within 3-4 days, your urine metabolite levels will be lower than if you hadn’t started losing weight and the more weight you lose, the bigger the difference will be between losing weight and not losing weight.

        It sounded like there were several weeks between when you started exercising and when you tested positive, so I tend not to believe that exercise was a factor. You probably would have tested positive for even longer if you hadn’t started exercising.

        There is another explanation…take a look at this paper: It shows that even without smoking, people’s urine metabolite levels are super variable from hour to hour and day to day. If you are around the cutoff, you can easily pass one day and fail the next day, especially depending on how hydrated you are.

  7. Tom says:

    So I have a drug test coming up soon. I have gone over 90 days and I have just recently passed an at home drug test. I had the time to quit since I knew my graduation date was coming (yay). However I am 100lbs overweight and i’ve decided to start taking better care of myself. No better time than when youre 30 right.

    I just want to make sure that its safe to do some exercise and start working at it before hand. Would you risk it?

    • Yes, you should go for it. The increase in blood THC levels after exercise is very small and transient. It lasts less than 2 hours and urine levels of THC metabolites don’t even seem to be affected. There is no reason you shouldn’t exercise for fear that it will cause a positive on the drug test.

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