Body fat plays an important role in how much THC and its metabolites accumulate in your body. What effect does this have on passing a cannabis drug test?

There are many strategies that people use to try to beat cannabis drug tests. Out of all of these, the effects of diet, exercise and body fat are both the most discussed and the most misunderstood.

What do others say about exercising?

“The point of exercising, in the context of drug tests, is to increase your metabolism and burn the fat cells that store cannabinoids.”

“Exercise is one of the only ways to effectively burn fat from your body. Since THC is stored in your fat cells, exercising can help you get rid of cannabis from your system.”

“Get as much exercise as your body can handle, at least a couple hours a day. Jog, run, speed walk, do calisthenics—anything you can think of.”

This is advice that seems to be universally agreed upon by the Internet. But is there any science to back it up? Just how important is body fat? How fast can diet and exercise clean your system of THC? Read on to find out.

Distribution of THC to Body Fat

Before I get into the effect of body fat on THC elimination, you should understand basic principles of THC pharmacokinetics – or how the drug behaves in the body.

  1. Absorption Phase (First 15 minutes): THC is rapidly absorbed from the lungs after smoking, driving an increase in blood levels.
  2. First Distribution Phase (15 minutes to 1 hour): THC levels in the blood drop rapidly as it distributes into organs and fat tissue.
  3. Second Distribution Phase (1 hour to 4 hours): An equilibrium is reached between THC in blood and in most organs. There is still a net movement of THC from blood into fat tissue since this occurs more slowly than with other tissues.
  4. Elimination Phase (4 hours and beyond). THC in blood and fat tissue reach equilibrium. As THC in the blood is lost to liver metabolism, there is a net movement of THC from fat tissue back into blood.

During the elimination phase, THC levels in the blood are dependent on two things:

  • The rate of THC metabolism by the liver
  • The rate of THC redistribution from fat tissue back into blood


I would like to clear up two misconceptions I frequently hear:

Fat Metabolism and THC Metabolism Are Different Processes

It’s great if you have a rapid metabolism (meaning that you don’t gain weigh easily). But this doesn’t mean that you will metabolize THC quickly. THC metabolism occurs almost entirely in the liver. It has no relationship whatsoever with your fat metabolism. It is a completely different set of enzymes that are regulated in completely different ways.

The difference between fat and skinny people in passing drug tests is related to THC storage in fat and has nothing to do with the actual metabolism of THC.

THC is Not Really “Trapped” in Fat

THC is not actually “trapped” in fat in the sense that it depends on the fat being burned to be released. THC (and other THC metabolites) are in a constant equilibrium between your blood and fat tissue. The THC molecules are always free to move back and forth between these tissues.  This process is completely passive and based on concentration gradients.

Percent Body Fat and THC Elimination

Now that you understand some basic principles of THC pharmacokinetics, let’s address how body fat impacts the elimination of THC and the ability to pass cannabis drug tests.

This is Skinny Bob. His favorite daily activity is to smoke a joint and cycle 30 miles. His body fat percentage is 10%. The ladies love Skinny Bob.

This is Average Bob. He likes to take rips from a bong and watch TV. He has a body fat percentage of 20%, which is about…average.

This is Fat Bob. Fat Bob doesn’t get off the couch much. He will smoke a blunt, get the munchies, and eat a Big Mac,  a bag of Cheetos, and and a pint of Ben & Jerry’s. Fat Bob has a body fat percentage of 30%.

Skinny Bob, Average Bob, and Fat Bob all consume the same amount of cannabis – they smoke one joint a day. We can use a mathematical model of THC pharmacokinetics to look at the THC profiles in the blood and fat of the different Bobs :

THC levels in blood and fat with daily cannabis use in people of different body fat percentages

You can see that the profile of THC in the blood is almost completely overlapping in people of different body fat percentages. Skinny Bob won’t get any more high than Fat Bob after consuming the same amount of cannabis.

However, there is a big difference in the accumulation of THC in body fat.

  • Skinny Bob accumulates very little THC in his fat tissue, even after a week of regular smoking.
  • Average Bob accumulates some THC in his fat, but this levels off after a few days
  • Fat Bob accumulates a lot of THC in his fat. It takes a week of smoking weed every day to reach maximum levels in the fat.

Here is the ratio of total THC in their fat to total THC in their blood after their one week of smoking.

Ratio of THC in fat to blood in people with different body fatThe Bobs all apply to a new job and get hired. Good job Bobs! Now they just have to pass a drug test to start working. They all take one last toke and then stop consuming cannabis.  Let’s take a look at the impact of their accumulated THC in fat on how long it takes to clear their system. I put the plot on a log scale to make it easier to see what happens at low THC levels.

THC pharmacokinetics after stopping cannabis in people with different body fat

As usual, the peak THC levels in blood after smoking a joint are the same in Fat Bob, Average Bob, and Skinny Bob. But what happens next is quite different. The extra THC that has accumulated in the fat of Fat Bob causes an extended time of THC elimination.

The THC stored in body fat is actually changing the half-life of THC elimination. Even two weeks later, there is still significant THC levels in the body of Fat Bob, although it has cleared out of the system of Skinny Bob and Average Bob.

Their THC metabolism is exactly the same. The dramatic difference in the THC half-life is purely due to how much THC is stored in their fat.

What About THC Metabolites and Body Fat?

Although THC itself is measured in blood drug tests, urine drug tests measure a metabolite of THC and not THC itself. However, this same principle still applies to the metabolites for two reasons:

  • The levels of THC metabolites are driven by the levels of THC itself – so extended elimination of THC will lead to extended elimination of metabolites
  • THC metabolites such as 11-OH-THC and THC-COOH are also very lipophilic (i.e. tend to distribute to fat) and so the same thing will happen with them – the more fat you have, the more the metabolites will accumulate and the longer the time of elimination from your body will be

Can Diet and Exercise Help You Pass a Cannabis Drug Test?

There is little effect of a single exercise session on blood THC levels – there is only a small and very transient increase (and no effect on the THC-COOH metabolite). However, one exercise session does not induce a significant change in body fat.

What about sustained diet and exercise that lead to a significant reduction in body fat? Can this help you pass a drug test? The general answer is that a reduction in body fat will help clear out THC and metabolites faster by reducing the tissue where they are able to accumulate.

Keeping body fat low will help most in regular tokers. For the occasional user, there will not be as much THC accumulation in fat, and so your body fat percentage will not matter much.

[Flickr/ yuan2003]

We do need a dose of realism regarding this as a strategy to beat cannabis drug tests. You cannot just lose water weight, it has to be actual body fat. If you have to take a drug test in a matter of weeks (or less), few people can achieve a dramatic reduction in their body fat so quickly.

Every bit helps, so I do think that diet and exercise are worth doing if you have sufficient time to actually lose weight before you are tested. The best recommendation though is to proactively keep fit – it is both healthier and you will be better off in the event that you are drug tested.

Questions? Please comment below!

Last modified: April 22, 2017

26 Responses to " Body Fat and THC – Can You Pass a Drug Test with Diet and Exercise? "

  1. Nice Guy says:

    I find the graphs here pretty useful. Personally, I found out that I had 2 weeks until a work drug test. I am a recreational user but had smoked probably 5 times that week. I am about 8% body fat, and hoping to avoid testing positive, I have started a ketogenic diet, drinking over 100 ounces of water a day, taking niacin, and working out for at least an hour a day. Hoping I beat this test.

  2. Tiffany says:

    Ok, so I have an important question. I quit smoking 4/29 And passed a drug screen 6/10. Since then I have lost about 25 lbs and then had a drug screen on 7/17, which was positive.i have not touched marijuana in approximately 10 weeks at that point. Does anyone have an explanation for that?

    • Prof of Pot says:

      There are 3 possibilities: 1) The first test was a false negative or the second test was a false positive. 2) The tests were correct, but you would have received the same results regardless of the weight loss. There is a ton of variability in urine concentrations of THC metabolites from day to day and even hour to hour. It is not impossible to test negative at one time and then test positive later week later due to this. This is especially true if people take precautions like drinking a lot of water right before the first test, then once they test negative, they relax and don’t bother for the second test. 3) The positive on the second test was because of the weight loss. Usually a month of weight loss isn’t enough to really matter, but you lost a very lot of weight in a short period of time. When I have a chance, I will put this in the mathematical model and see if it could potentially increase the chances of a positive test.

      • Tiffany says:

        Ok, but like I said, I haven’t smoked since 4/29. The weekend prior to the second test, I was taking Aleve pm, because I’m an insomniac.i also have ptsd, panic disorder, adhd, and stress induced anorexia. That is the reason I was smoking in the 1st place. Due to my career, I can not have a weed card and renew my license for my job, since they both are processed through the state. Benzodiazepines make me sick, sleep aids make me to groggy but I’m ok with ADHD medication (except they make my appetite almost nil). I should definitely not be testing positive, unless the nsaid could give a false positive. I did a urine test at on the 21st and it was negative…im so confused.

        • Prof of Pot says:

          The NSAID should not cause a false positive. They test for assay interference with commonly used drugs.

          I did use the model in this article to predict what would happen if someone lost a lot of weight after they quit smoking. I’m going to write up the results in another article, but basically there is a very small (1-2%) increase in THC levels at first, and then within a few days, they start to go down.

          I can’t say why you tested positive so much later after testing negative, but I really believe that your levels would have been even higher if you hadn’t lost the weight.

  3. Bobby says:

    Do you think donating plasma would help eliminate thc from the body? Would it cause thc to leave fat for the blood once the concentration had decreased following plasmapheresis? Saving lives and passing drug tests would benefit all!

    • Prof of Pot says:

      Yes, plasma donation by plasmapheresis will remove a lot of the THC in the blood, and then some THC will move from fat to blood to equilibrate. Will this help you pass a drug test significantly sooner? It depends on the individual, but probably not by much. There is just so much more THC stored in fat than in the blood. Now if you could schedule the plasmapheresis for immediately before the drug test, that is a different story! Maybe a plasmapheresis center could be opened next to every drug testing center with appointments on demand.

      • Bobby says:

        Haha amazing. If I were to donate right before the test, would that encourage even more to go into my blood that day and then filter into my urine? I wonder how long that takes. Thanks so much for answering my questions, and again for your website.

  4. Jeff says:

    Prof of Pot,

    Thanks for taking the time to break down the science of this important topic. Like others, I recently found out that I need to take a pre-employment drug screen for a new position. I’ve been smoking regularly as a patient in California for the past two years. The last time I smoked was on 7/16 and I have to take a test by 8/10.

    I exercise regularly (running 5-6 miles a day) and have 15% body fat. Based on the model, I consider myself “Average Bob”. My question for you is, is it realistic to assume that I should be able to consistently pass a test with 25 days of not smoking, the right diet, and tons of exercise? I am planning to start a charcoal cleanse as well, in hopes of improving my chances.

    Any wisdom you could provide would be greatly appreciated.


    • Prof of Pot says:

      Hi Jeff,
      There are no guarantees – everyone really is different. It depends highly on how much you smoke (regularly could mean once weekly or twice daily). 25 days is sufficient for most people though. The charcoal will help as well as drinking plenty of fluids right before the test. I recommend buying a set of home test kits and testing yourself regularly so that you know how long it takes for you to clear your system and so that you can go into the real test with confidence.
      Best of luck!

      • Jeff says:

        Thanks for the prompt reply. By regularly I meant 1-2 bowls a day , 4-5 days a week of high potency THC medical marijuana from California. I’m happy to hear that 25 days is sufficient for most, and I’m taying cautiously optimistic. I’ll continue my regiment and be sure to post the results here to hopefully help others in a similar situation.

        • Prof of Pot says:

          Here is another resource for you: There is still some risk of a positive without taking additional steps. The charcoal should help though.

          • Jeff says:

            Thanks for the tip. I’ve heard in the past to not really trust these calculators, but this one seems somewhat helpful for time estimates.

            I’m in the unique position in that I already have an existing relationship with the hiring manager for my new job. And they are aware of my situation. Fortunately, I can probably request an extra 15 days to be 100% for my test, but I’m trying to avoid that.

            I do have a follow up question regarding the charcoal. What is position on volcanic ash drinks? Such as Sonne’s #7? It seems like it would have the same affect as charcoal but to a lower degree.

            Thanks again for your responses.

          • Prof of Pot says:

            You definitely have to take the calculators with a grain of salt.

            I don’t think volcanic ash drinks will work. The Sonne’s site says that it adsorbs molecules based on charge (it is negatively charged and it binds molecules that are positively charged). No THC metabolite is positively charged.

  5. Anonymous says:

    It’s good to find to find someone who actually know s about pharmacology a little bit and a lot about the related field of pharmokenitics instead of Finding forum after forum saying there experience is 20 years of smoking with no absolute Scientific evidence to back their claims it’s nice to have finally found someone who knows what they are talking about 👍

  6. G says:

    I have 3 to 7% body fat and i work out all day as i trim palm trees everyday in 95 degree heat and consume at least 1 gallon and a half of juice and water daily. I have been a daily smoker for awhile now. How long do you think it would take to clean out if i stop today

    • Prof of Pot says:

      I can’t give an estimate because there are too many variables and everybody is different. You have super low body fat, so for the amount you smoke, it should be cleared much faster than average. The best way to know how fast you clear it is to buy a bunch of at home drug tests and take one once a week or so until you see that you are clear.

  7. bill says:

    Hi Prof Pot

    My question is this: I was clean for around 9 to 10 months. I then smoked 2-3 small hits high potency a day for a month and a half. (Around 7-8 grams total in that 45 days) I weighed 215 lost 10 pounds and weight 205 now. im 38 with average metabolism. Ill be testing around 90- 95 days clean. Will I be good? Any advice is extreamly appreciated. Thanks Professor

    • Prof of Pot says:

      Chances are that you should be, but I would buy some at home drug tests and check yourself before the real test. If things aren’t looking good, then try to lose more weight, use activated charcoal, and hydrate well on the day of the test.

  8. Ivanb says:

    My friend tricked me yesterday with 3-4 vapes of thc which I have never use before. I’ll have drug testing on the next 2 months. I’m 6.0, 75 kg, with 15-20% of body fat. I exercise regularly. Do you have any advice to help me pass this drug test. Thx

  9. John says:

    I need to take a baseline health test with my urine drug test. I am supposed to fast for 9 hours before i go in for my blood test so that my blood sugar and other things are at a normal rate… do you know if a same day detox drink will throw off these tests? I should be able to be clean for about 25 days but have been a daily user of concentrates for almost a year and then herb for several years before that? I believe the detox will have vitamin b in it which could throw off my triglyceride. I workout regularly and am more muscular than fat. Have had abs my whole life.. any advice would be helpful thanks!

    • Prof of Pot says:

      Sorry, I can’t give you a good answer on this. It all depends on what is in the drink and how much of it. They really should list ingredients. You can always mention to the clinic that you “accidentally” took your vitamin B pill that morning.

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