How Long Does Marijuana Stay in the Bloodstream?

This chart shows how long does weed or cannabis smoking or other use cause THC to remain in the hair and body and how much time after smoking you could be testing positive.

Many marijuana enthusiasts need to know how long does THC stay in the blood system?  The simple answer is up to 30 days. It is rare that marijuana is detectable in urine after 30 days of abstinence. It may be detectable longer in hair, but such tests are infrequent and unreliable. However, many factors which we will examine determine specifically how long weed stays in your bloodstream. How Long Does Marijuana Stay in the Bloodstream

Smoking frequency, the biggest factor in how long marijuana lasts in the blood

How often and how much you smoke is the biggest determinant of how long marijuana stays in your blood. A review published in 2006 by the University of Missouri showed some promising results for those anxious about how long THC will stay in the blood.

Most drug use detection for pot is done by means of urine testing. The scientific review found that for the average bud smoker, THC will leave the body somewhat quicker than commonly assumed.

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For example, for a single-use or infrequent use, THC-COOH, the metabolite tested for in urine, is not detectable after merely 72 hours for the average person.

For most chronic users, the average person will test clean in about one week after abstinence.

Most heavy users are looking at 10 to 21 days of abstinence before THC levels test clean.

Frequency of use How long for a clean test for an average person
Single or infrequent 72 hours
Chronic use 7 to 10 days
Heavy Use 10 to 21 days
All use  Less than 30 days

Though some people on the extremes of their ability to store and metabolize THC may get wide variations, for the average person, marijuana stays in your blood for less than 30 days.

What determines how long does THC stay in the blood system?

stay in blood

How long weed stay in your blood system is determined by your biology, the amount and frequency of exposure, and the amount of THC stored in fat cells. Many users know that THC stays in the bloodstream by hiding in fat cells, which then release variable levels of the THC metabolite THC-cooh (11-Nor-9-carboxy-THC) over time. This metabolite which results when the hash or cannabis you have consumed is processed by the liver is what is tested for in your urine.

What to do before the test to reduce THC levels

Follow these steps:

  1. Reduce or eliminate calories and drink lots of water so the THC begins to flush from your fat cells. Do this at least 4 days out from the test.
  2. Drink lots of water to flush the THC out in your urine, at least 3 days out from the test, all the way up to test time.
  3. Re-feed. Two or three days before the test, raise your calories back to normal to stop the fat from burning and releasing THC.
  4. Pre-test. Get a marijuana test from your local drug store and make sure it’s negative before you go to the scheduled drug test. If positive, you will have to find a way to stall or re-schedule.

The amount of THC in your urine will be determined by how much weed is in your fat cells and how quickly it is clearing out of the fat cells, into the body, then into the urine. The rate of fat burning is determined by your diet and exercise. If you have a drug test coming up and a few days to prepare, it is advisable that you first fast, eat low or no calories for a few days so the remaining THC empties into the body, then drink lots of water to clear it out of the system. Before the test, you will need to put a stop to the fat-burning by consuming sufficient calories. This will put a halt to the THC spilling out of the fat cells, into the blood and urine. Next, to dilute the remaining THC, drink lots of water. To recap, fast, hydrate, then refeed, and hydrate. This will flush the THC from your system and dilute the remaining cannabinoids before the test.

What not to do

  • Don’t show up hungry (THChc will leak from fat cells)
  • Don’t use masking agents (inconclusive tests make you look guilty)
  • Don’t go in thirsty (marijuana will concentrate in your urine)

Some people will try to drink masking agents to prevent the test from detecting THC. We advise against this because the test can sometimes discover the masking agents and also, an inconclusive test is sometimes seen as a failed test, especially if it is also inconclusive on a retest. That’s the sign of a masking agent and suggests guilt. Since the scientific review we cited earlier suggests the average person will get rid of THC fairly quickly, it’s better to be prepared, clear the system out by fasting and flushing.  Then as the most important suggestion, buy a home-test from a drug store, and test yourself to make sure you don’t test positive before you take the scheduled test.

Also, don’t go into the test hungry and in fat-burning mode, because THC will be spilling out of your fat cells, into the bloodstream, and into the urine. Instead, make sure you have been well fed and drinking lots of water for a day or two and on test day. If you are thirsty, your urine will be more concentrated and that could concentrate the THC and lead to a positive test.

Pre-test before your drug test

Don’t go blindly into a scheduled cannabis drug test. The drug tests for weed that you can buy from your local drug store is often the exact same test you will face when you get drug tested. So, make sure you test negative before you go into the test. If you are positive, try to reschedule your test, fast and flush, then pre-test again until you are negative. Then go into the rescheduled test. Although this method, fast, flush, and pre-test, will succeed most of the time, there is a small chance to test positive after having tested negative at home. This happens if you let your calories get too low right around test day and THC begins to leak from the fat cells that the body is burning for energy. So, remember to stay hydrated and well-fed on test day and keep up the good fight to make medical marijuana accepted so that in the future, such tests will be unnecessary.


— CARY, P.L. and — NATIONAL DRUG COURT INSTITUTE (U.S.), — The Marijuana Detection Window: Determining the Length of Time Cannabinoids Will Remain Detectable in Urine Following Smoking: a Critical Review of Relevant Research and Cannabinoid Detection Guidance for Drug Courts. — National Drug Court Institute.

This article about Medical Marijuana was published on and updated on May 21, 2020 . Medical facts in this article was checked and article was medically reviewed by our . Author of this checked article is
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