A scientific breakdown of the claim that you can clear your system of THC and pass a cannabis drug test by sweating. Is this a myth or reality?

In attempting to pass a drug test, people will try almost method. Unfortunately, much of what you read about ways to beat drug tests are misinformation.

One commonly cited method is to sweat out THC by exercise or use of a sauna. I have seen this repeated on so many cannabis websites and message boards. Here is just one example from newhealthguide.org:

“The THC present in your fat cells is also excreted through your sweat and you can increase the excretion by using a sauna. The heat from the sauna helps in dilating the blood vessels and capillaries, so that the blood reaches the fat tissues and let THC excrete through the sweat.”

It is a nice thought that we can relax in the sauna as our THC is effortlessly sweated out. But does it actually work? Read on to find out the truth.

What is Sweat?

Sectional view of the skin with sweat glands highlighted [Wikipedia]

Let’s start with the basics. Sweat, also known as perspiration, is aqueous fluid secreted from sweat glands of the skin. Sweating is primarily used as a means to cool the body.

We typically lose about 300 to 700 mL of sweat per day from 2 to 4 million sweat glands over our bodies. However, we can lose up to 2 liters of water per hour during exercise.

The water in sweat comes from plasma (which is the aqueous part of our blood). Other molecules from our plasma can diffuse across the membranes of sweat gland and go into sweat as well. In fact, many drugs are detectable in the sweat of users, including opiates, amphetamines, and cocaine.

Are THC and Other Cannabinoids in Sweat?

After consumption of cannabis, your body immediately starts to metabolize THC as shown below. Urine drug tests detect the final metabolite in this pathway. Since all of these metabolites contribute to detection of cannabis use, it is important to determine whether they are found in sweat as well.

The main metabolic pathway of THC. THC-COO-glucuronide is excreted into the urine and detected by drug tests.

THC

A study has shown that THC is indeed present in sweat. However, due to the way that the sweat samples are collected (with a wipe or patch on a limited amount of skin), we cannot easily determine the total amount of THC excreted in sweat over the entire body.

11-OH-THC

In one study, this metabolite could not be detected. That doesn’t mean that there is none at all in sweat, just that levels are so low that they are below detectable limits. This makes sense, since plasma levels of this metabolite are very low (except right after taking edibles).

THC-COOH

In the same study as above, this metabolite was not detected in sweat. At first it’s surprising since within a few hours after smoking, its plasma levels are several times higher than THC.

If THC-COOH levels are even higher than THC in plasma, then why can’t THC-COOH be measured in sweat? The answer lies in the relative pH of plasma and sweat and the ionization of this metabolite.

At the pH of plasma (7.4) the majority of the metabolite is in its ionized state (THC-COO-). With its negative charge, this ionized form cannot cross membranes to get into sweat. On the other hand, sweat is acidic (pH=5.0), which will convert this metabolite to its unionized form (THC-COOH), where it can easily diffuse back into plasma.

THC-COO-glucuronide

THC-COO-glucuronide is formed by attaching a glucuronide sugar molecule to THC-COOH. This metabolite is large and polar, which means that it cannot cross membranes by diffusion. Although there have been no attempts to measure it in sweat, there is no reason to think that it could get into sweat.

Can You Beat a Drug Test By Sweating Out THC?

It is easy to see how the idea got started that you can pass a drug test by sweating out THC. After all, it is there in sweat. So the more you sweat, the more THC you eliminate, right?

The truth is that although THC is excreted via sweat, it is a whole other matter whether you can actually sweat out enough to beat a drug test. After all, the methods used to detect THC in sweat could measure incredibly tiny amounts. If you are not sweating out significant amounts of THC and its metabolites, then it will not make a difference.

Nobody has yet performed a scientific study to assess whether sweating will reduce THC and metabolite levels in your body or whether it will help you pass a cannabis drug test. However, we will use our powers of scientific deduction to see whether this is even feasible.

  • THC is excreted in sweat, but none of its major metabolites are. See section above for the in-depth explanation. The THC molecule itself only represents a fraction of the total load in your body that will eventually be excreted into urine and detected by a drug test.
  • THC is stored much more in fat than in plasma. The ratio of THC in fat versus plasma is at least 100 to 1. Let’s say you spend an hour a day in the sauna and sweat out 2 liters. It won’t matter much because there is such a small fraction of your body’s THC in aqueous fluid such as plasma.
  • THC is highly bound to plasma proteins. 97% of THC in your plasma is not floating freely, but is bound to plasma proteins. Only the 3% fraction that is free is available to diffuse across sweat gland membranes into sweat.

Can Hyperthermia Speed Elimination of THC?

What if exercise and sauna do work to eliminate THC, not because of sweating, but because of increased core or skin temperature? The sauna can raise your core body temperature by 1 degree Celsius and your skin temperature by up to 4 degrees Celsius.

These temperature increases do elicit several adaptive changes (besides sweating) in your heart rate and blood flow to various organs. However, a review of the scientific literature found no consistent change in drug elimination as a result.

Conclusion on Sweating out THC

There is no evidence that a significant amount of THC or its metabolites can be excreted in sweat. Given all of the above information, beating a urine drug test by sweating THC out of your system is a myth. No matter how much you sweat by exercising or the sauna, you will lose a negligible amount of THC.

Interested in learning more about drug testing? See whether drinking extra water or exercise helps flush out THC.

[Featured image: Flickr/ Thomas Wanhoff]

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Last modified: April 23, 2017

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