Can you flush your system of THC and its metabolites by drinking lots of water or other liquids in order to pass a drug test for marijuana? Or is this myth?

The Controversy of Drinking Water to Flush Out THC

Today I am focusing on another common marijuana drug testing belief: that you can “flush out your system” of THC and its metabolites by drinking lots of water or other liquids (I will refer to this as hyper-hydration)

Don’t confuse this with drinking water immediately before the test to dilute the urine (which is a whole different topic). This is referring to drinking lots of water in the days and weeks leading up to  the test with the hope that more THC or metabolites will be cleared out.

The hyper-hydration claim is highly controversial. About half of websites recommend it and the other half claim that drinking excess water will not help you pass a marijuana drug test.

For example, jezebel and wikihow fall into the pro-hydration camp (if you are getting your drug testing advice from wikihow, please stab yourself in the eye with a fork):

“Drink 20 to 40 ounces of sports drink per day to restore your electrolytes and keep you hydrated. Drink roughly 1 gallon (3.8 L) of water to flush your body of toxins. Drink the tea and other diuretics throughout the day as well.”

“Drink lots and lots and lots of water—gallons of it—from the time you learn about your test up until the big moment.”

On the other hand, and fall into the anti-hydration camp:

“Drinking plenty of water several days before the test is of no use. Water does not help clean the THC accumulated in the fat cells.”

“…drinking excess water does not help your body eliminate marijuana and its metabolites from your body, nor does it speed up this process.”

I love scientific controversy! But you probably just want to know whether it is worth the trouble of pissing every 30 minutes for the next two weeks so you don’t lose your job. Fair enough, let’s get this settled.

Nobody has ever studied whether hyper-hydration affects elimination of THC or its metabolites. However, we can still use our knowledge of pharmacology and physiology to arrive at an answer for whether drinking a lot of fluids has any chance of helping you pass a drug test for marijuana.

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


Basics of Drug Excretion by the Kidneys



These are your kidneys. One of their jobs is to remove toxins, including drugs, from your blood. It does this by the process of renal excretion. There are several important processes involved in renal excretion that are relevant for our discussion today:


  1. Filtration: Your kidneys use a filtration system where your plasma (the aqueous part of your blood) is filtered into the renal tubule. About 20% of the plasma that goes to your kidneys is filtered.
  2. Reabsorption: After a molecule is filtered into the renal tubule, it can be reabsorbed back into the blood. Any molecule that can easily cross membranes (and most drugs can) will be highly reabsorbed.
  3. Secretion: Some molecules are are actively pumped  from the blood into the renal tubules by transporters.


How Hyper-hydration Affects Renal Excretion

The effect of hyper-hydration on the elimination of THC and its metabolites has not been studied, but we do understand how it affects the processes of the kidney.

Many people would think that drinking a lot of water would increase filtration rate. However, one study showed that in the short term, high hydration decreases filtration rate, and another study showed that drinking extra water has no effect at all on filtration rate over the long term.

Once you understand how the kidneys control the amount of urine production, it actually makes sense that filtration wouldn’t change by drinking more fluids. The water filtered by your kidneys into the renal tubule is almost entirely reabsorbed. Your kidneys do not need to create more urine by increasing filtration, they do it simply by reabsorbing less water.

What is the impact of hyper-hydration on the reabsorption of drugs and other molecules? In several cases, a modest decrease was observed in reabsorption. Why? As water is reabsorbed from the renal tubule to the blood, the drug becomes more concentrated in the urine. This concentration gradient drives reabsorption of the molecule into the blood.

When less water is reabsorbed, there is less of a concentration gradient and also the urine flow is faster, so there is less time for the molecule to cross the membrane into the blood. The net result is that drinking extra water can reduce reabsorption, which may modestly increase renal excretion of some drugs.

There is no evidence that hyper-hydration can affect renal secretion, because it is an active process that does not depend on a concentration gradient.

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


Does Hyper-hydration Increase Excretion of THC and Metabolites?

Here is the basic metabolic pathway for THC (for more details, read our guide to metabolism of THC):

THC metabolism

There are two important factors for whether hyper-hydration could possibly increase elimination of THC or any of these metabolites to a significant extent:

  • Is it reabsorbed?: As explained above, hyper-hydration increases renal excretion only for molecules that undergo reabsorption.
  • Is renal elimination a significant percent of total elimination?: Renal elimination is just one pathway for drug elimination. If other elimination pathways happen much faster than renal elimination, an increase in renal elimination will have little overall effect.

So let’s apply each of these criteria to the four THC molecules:

THC metabolites renal elimination effect hydration

Assessment of whether drinking water can possibly effect excretion of THC and metabolites in urine

As you can see, 11-OH-THC and THC-COO-glucuronide do not undergo reabsorption. Therefore, there should not be any effect of hyper-hydration on them.

THC and THC-COOH do undergo reabsorption, so it is at least possible that drinking a lot of water will increase their elimination. However, to what extent? Renal excretion contributes <1% to the total elimination of each. Data from other molecules indicates that hyper-hydration increases renal excretion by about about 1/3. Even if we increase renal excretion by 10 times, renal excretion of THC and THC-COOH will still be insignificant relative to other pathways.


 Myth Busted?

Nobody has yet tested the effect of drinking a lot of water on flushing out THC and metabolites from your body. However, we assessed whether it is even possible using our knowledge of the physiology of the kidney and cannabinoid pharmacology. Our analysis shows that drinking extra water cannot have a major impact on the elimination of THC or its metabolites. This myth is busted, but you should still stay well hydrated!


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

[Featured image: Flickr/ Eduards Pulks]

Last modified: September 11, 2017

13 Responses to " Drink Water to Flush Your System of THC – Drug Testing Myth? "

  1. paul says:

    Drinking water worked for me!

  2. Kgl says:

    3 gallons of water 2 days with 2000 mg of Niacin

  3. Phil says:

    Is diluting your urine with lots of water and consuming high levels of vitamin B a viable option to passing a test (at
    least passing the eye test)?

    • Prof of Pot says:

      Yes, absolutely. Everyone should dilute their urine by drinking lots of fluids right before the test. B vitamins will take care of the color, but they may also test for specific gravity and creatinine, which will be affected by dilution. I am going to write an article soon with details of how to get around this.

      • Josh says:

        Buy creative supplement in the store to keep levels high duh

        • Prof of Pot says:

          Well yeah, the short answer is take a creatine supplement. But the question is how much to take and how long before the test to take it? This wouldn’t be obvious to most people.

      • Jay says:

        I have used the temporary water dilution method after only a week of not using. Btw, I am a daily user. I drank lots of dark roast coffee and water throughout the prior day, and a good portion of the night. The morning of the test, I drank 30 ounces of water around 6am, the test was at 9am, and ate a 6″ sub with high sodium meat around 7:30am to slow my metabolism. By the time I was due to turn in a sample, I had already urinated about 6 or 7 times that day. I avoided the beginning and end of the stream, only turning in the middle stream. To my delight, it worked and I got my first professional job. I have since used this technique once more and it yielded the same results.

  4. Chezabel says:

    What about over hydration in an effort to dilute urine in an effort to make it fall below the detection threshold (ng/ml)?

  5. Marcus says:

    First off you can call it “diluting” but it’s just overloading your bladder where your liver will excrete the opiates or drugs from your system when drinking water. How you ask bc all your going to piss out is water, legit just water where there are no additives (drugs or anything like it) in your urine. Doesn’t mean you’ll pass just means it will come out inclusive. Oh and I work for a drug testing company.

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