Cannabis can stay in your system for a surprisingly long time. For chronic consumers, weed stays in your body for up to a few weeks. Yet, unfortunately, getting an exact time frame is challenging. Every person processes cannabis differently, and testing technologies produce variable results. However, data from the last three decades provides some educated estimates as to how long the herb sticks around. Here’s how long you can expect to test positive for the herb.
How long does weed stay in your system?
In general, the more cannabis you consume, the longer it will take to leave your system. Fortunately, those who smoke the occasional joint or partake in the herb at a rare event don’t have much to worry about.
Most estimates suggest that it takes around three days for the herb to clear your system before a urine test. Unfortunately, heavy cannabis consumers may have a more difficult time.
Drug Court research from 2005 suggests that most cannabis consumers will pass a urine test in about 10 days. Heavy consumers, however, may take up to 21 days. The authors write,
Recent scientific literature indicates that it is uncommon for occasional marijuana smokers to test positive for cannabinoids in urine for longer than seven days using standard cutoff concentrations.
Following smoking cessation, chronic smokers would not be expected to remain positive for longer than 21 days, even when using the 20-ng/mL cannabinoid cutoff.
This study argues that occasional consumers will likely pass within three to four days.
Older studies using dated technology have found slightly different results. Cronic consumers can test positive for cannabis in a urine test over two months after their last taste of the herb. One 1985 study found that chronic consumers could test positive up to 77 days after leaving cannabis behind.
For all study participants, the average amount of time was 27 days in urine tests. A later study had a similar finding. The research, published in 1989, found that it took 13 heavy cannabis consumers up to 25 days for the herb to clear their system.
So, the golden number? Evidence suggests that it takes heavy cannabis consumers up to one month to pass a urine test. Generally speaking, samples that test positive after the 30-day mark are not very common.
With this information, most routine cannabis consumers can expect a clear urine result after a few short weeks of cannabis abstinence.
A few caveats
The 30-day cutoff has a few important caveats, however. Every person will process cannabis a bit differently. Depending on individual metabolism and lifestyle, some moderate consumers may still fail a urine test, even if they have waited a couple of weeks before submitting samples.
These numbers also change depending on the type of test used to check for THC. The urine test is the most common drug tests around. The test measures the levels of THC metabolites that have been secreted in urine.
It does not test for the presence of THC itself. There are also different types of urine tests available. Whoever ordered the test will be able to select the acceptable concentrations of THC metabolites.
Say, for example, that your urine sample initially tests positive for a THC metabolite called THC-COOH. Laboratory professionals will then test to see how much of the metabolite is actually present. If the urine screens less than 20-nanograms per milliliter of THC metabolite than you would pass the test.
Some testers screen at the 50-nanogram mark. The nanogram testing limit can be quite variable.
Different drug tests have different results
Blood testing and hair follicle testing are the next most common tools to evaluate cannabis consumption.
Unlike urine testing, blood testing does not show past cannabis consumption. Rather, THC will only stay present in the blood for up to one to two days after consuming on a single occasion. Heavier cannabis consumers will have to wait up to one week to pass a blood test.
A blood sample is a good test of whether or not someone is using cannabis at the present moment, or within a very recent time span. It does not show you whether or not someone has a long-term history of consumption.
However, they cannot give too much of an indication of someone’s history with the herb. In some states, blood testing is used to rule out cannabis-intoxicated drivers. Many blood tests use a five-nanogram limit when testing for the presence of THC.
However, studies conducted by the American Automobile Association (AAA) have found that these roadside blood tests are ineffective ways to test for impairment, and do not reflect scientific research on the subject.
Hair tests are perhaps the least common test of cannabis use. THC metabolites begin to show up in the hair about one week after consumption. Hair holds onto bodily information the longest. Cannabis compounds can be found in the hair for up to 90 days after consumption, which is the most common cut-off point for hair follicle tests.
Here’s how about long it takes to clear cannabis before the most common tests:
- Urine test: 3-77 days (10-30 days for regular consumers)
- Blood test: 1 to 7 days (1-2 for light consumers)
- Hair test: 90 days
For more information on what to do if you are being drug tested, check out the article here.
Why does weed stay in your system so long?
Cannabis stays in your system for a long time because cannabinoids (cannabis compounds) are stored in fat cells.
THC and other cannabinoids are fat-soluble, meaning that metabolites of the compound are tucked away in fat and saved for later. This means that the active compounds in cannabis, cannabinoids, can slowly build up in the body.
In rodent tests, THC was found in fat cells up to 28 days after initial consumption.This fat storage means that cannabis can hang around for quite a while.
Not only that, but THC can be re-released into the blood stream periodically after exercise. This phenomenon was first exemplified in 2013 study published in Drug and Alcohol Dependence. The found that blood levels of THC increase after exercise.
Why? The theory is that THC is stored in fat, and when that fat is burned, THC is released into the blood and re-circulated.
The study tested fourteen cannabis consumers after 35 minutes of exercise. After 35 minutes, blood levels of THC increased by around 15% for a grand total of two hours.
This research also suggests that body mass index (BMI) can influence the THC released during exercise as well. Participants with a larger BMI had more measurable THC in their system.
The results of this study are corroborated by 2014 research among six cannabis consumers. Though, this study argued that the slight elevation in THC post-exercise is not likely to be reflected in a common drug test.
Those hoping to pass a urine test may have to wait a few weeks to test clean. Regular cannabis consumers can test positive for cannabis in their systems between 10 and 30 days on average.
However, these numbers vary depending on how THC levels are measured and how much cannabis is consumed. These numbers will also change depending on the unique biochemistry of the individual.
Those trying to eliminate THC from their system once and for all may have some waiting ahead. The compound is stored in fat, and it is slowly re-released back into the bloodstream as fat burns.
This could take several weeks and up to several months, depending on levels of activity and the total amount of cannabis consumed. Though, there are no precise estimates for this phenomenon.
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