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!

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Last modified: April 22, 2017

2 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.

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