How long does cannabis stay in your system?
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While a high might only last a few hours, cannabis can linger in your body for days after you consume it, experts say.
But exactly how cannabis works its way through your system is a complicated question. Here’s what we know.
Smoking or vaping cannabis is a “very efficient way to get the drug into your bloodstream,” said Dr. Robert Mann, a senior scientist at the Centre for Addiction and Mental Health.
Studies that he is working on and hopes to publish soon find that people reach a peak level of intoxication within about five minutes of smoking cannabis. “Then THC levels will decline over the next couple of hours very rapidly, then that decline slows off for a while, and then after several hours, I think the levels in the blood are quite low.”
The Canadian guidelines for lower-risk cannabis use recommend that you don’t drive for at least six hours after smoking cannabis, as that’s about how long impairment might last, he said, though obviously if you’re still feeling intoxicated after that, you still shouldn’t drive.
A number of things could affect how intoxicated you get after smoking cannabis, said M-J Milloy, the Canopy Growth professor of cannabis science at the University of British Columbia, and research scientist at the B.C. Centre on Substance Use.
These include the specific type of cannabis — for example, if it’s high in THC, an intoxicating chemical — how much you smoke, and exactly how you consume it. While smoking or vaping cannabis has a very quick effect, he said, it takes longer to feel an effect if you eat it — up to two hours after consuming.
“Cannabis’ effect on individuals as well as its detectability really varies by what people are using,” he said. “And if they are, for example, smoking high-THC joints, that’s a different thing than if they are taking gel caps of high-CBD cannabis.”
There is a lot of variability in the peak THC levels that different people reach, said Mann, and he also attributes that partly to things like “how deeply you might inhale, how long you hold the inhalation for and things like that.”
WATCH: Critics claim roadside marijuana testing flawed
THC levels in the blood don’t correlate smoothly to intoxication the way alcohol blood levels do though, Milloy said. “The bottom line is there is no blood test, urine test, etc. for intoxication.”
Although some Canadian police forces use a roadside test to detect the presence of THC, various critics including Milloy say that a positive result wouldn’t necessarily indicate that the person was actually impaired while driving.
While legal tests for cannabis intoxication exist, Milloy said, “I would argue that they are not based on good science.” He expects many cases based on these tests to end up being argued in court.
But once you’ve stopped feeling impaired, that doesn’t mean that the cannabis is totally gone from your body.
“When you use cannabis, the THC gets absorbed into the fat in your body, and so there’s kind of a reservoir there that keeps getting released fairly slowly, so that you will find trace amounts of THC in the blood for a longer period of time, but at very low levels,” Mann said.
Exactly how long it remains, though, is still a matter of debate. An article on urine drug screening by the Mayo Clinic suggests that cannabis can be detected in urine for between three and 30 days. A literature review — admittedly of mostly very small studies — suggested it’s more like one week to 21 days, depending on what kind of THC concentration cutoff you use.
The urine drug test that Milloy uses in his lab is supposed to detect cannabis use within the last 28 days, he said.
WATCH: Is weed good or bad for you? Everything we know about the health effects of cannabis
Part of the variation comes from how frequently someone uses cannabis, Mann said. “If you’re a frequent user, there are people who use daily or several times a day, it builds up in your system. It’s in your body at higher levels for a longer period of time just because it’s building up in the body.”
A very occasional user will eliminate THC from their system much faster, the studies show.
There’s still a lot of research to be done on how cannabis is processed, though, Mann said, such as how edibles change the equation, or how long other chemicals found in cannabis like CBD can be detected.
“There’s a lot that we know. It’s not the case that we don’t know anything. But there’s a lot that’s new and a lot that’s still needing investigation.”
How long cannabis can be detected in your system depends on a number of factors.
How Long Does Marijuana & Cannabis Stay in Your System (World’s #1 Resource)
In an effort to provide the most accurate answer for how long marijuana stays in your system, we set up a simple submission form where people can report their pass/fail drug test results, along with biometric measurements in addition to their smoking habits. This study started in 2011 and was used to create the only statistical drug test passing probability calculator.
Since then, we’ve continued to use the thousands of responses to update and increase the accuracy of our calculator formulas, and have released a detailed report of our drug test submission data with a state-by-state breakdown of drug test rates and racial discrimination. In response, we’ve started a change.org petition in order to raise awareness and bring an end to drug testing altogether.
After reading this information, use the calculator to determine your odds of passing a drug test and please consider taking the time to sign our petition (links below). For those interested in methods used to increase your odds of passing a drug test, our research comparing detox products and water dilution may be of use.
Passing Probability Calculator
Use the world’s only data-driven marijuana drug test passing probability calculator in order to determine your odds of passing a urine drug test. With over a decade of research and development, this is the only application that can provide an accurate answer to how long cannabis can be detected in your system:
The calculator graphs your Passing Probabilities vs. Days for untampered and diluted/detoxed urine. View Patent US 13/866,015 for more information.
Table of Contents
Tetrahydrocannabinol, commonly known as THC, is the primary chemical compound found in marijuana that is responsible for the euphoric “high” that cannabis consumers experience. It is an extremely hydrophobic (water fearing) organic compound that is metabolized and broken down by the body into about 80 different metabolites.
Because of the hydrophobic nature of these metabolites, polar molecules like water do not “stick” to and dissolve them, like they do when breaking alcohol and most other substances down. Instead, these metabolites associate themselves with non-polar compounds, such as alkanes, oils, and body fat – where THC and related molecules are stored to be metabolized and broken down at a later time.
Five metabolites of tetrahydrocannabinol, with THC-COOH being the primary one, are targeted by a multi-billion dollar drug testing industry that specializes in making money off of invading the privacy of people at every corner; pre-employment, medication pain pill contracts, insurance benefits, companies trying to evade payment of pension/retirement plans, etc.
This is one of the reasons why we set up this petition to end marijuana drug test discrimination. Unfortunately for those of us that use cannabis, it takes a considerable amount of time for these compounds to drop below detectable levels.
THC Concentration Levels After Consumption
Smoking is a very common way to consume cannabis. After inhalation, tetrahydrocannabinol (THC) quickly enters the blood stream through the lungs. With rapid circulation of the blood, this compound, in conjunction with a myriad of others, including CBD, act almost instantly on the human endocannabiniod system by interacting with CB1 and CB2 receptors located throughout the body.
THC has been found in studies to be immediately detectable in the body, with blood levels of THC reaching a peak at around nine minutes into smoking. For low-dose cannabis use, it can take between 3 to 12 hours for THC to drop below blood detection limits and from 6 to 27 hours for high-dose users.
It should be noted that the subjects of this referenced study were not regular marijuana smokers, which may explain why THC levels in the blood didn’t last much longer than a day.
Generally, active THC blood concentrations decrease rapidly after you finish smoking due to its fast uptake into tissues. However, if the uptake tissues are saturated with THC, it isn’t uncommon for blood levels of active THC to remain high for several days in chronic marijuana users.
Over time, these fatty tissues leach active THC molecules back into the blood stream (increasing the blood detection window), where the liver continues metabolizing them into non-psychoactive, THC-COOH derivatives for your body to pass (increasing the urine detection window). For chronic users, a background level of detectable THC can almost always be found in blood and urine for days.
Likelihood of Being Drug Tested by Ethnicity
Marijuana Detection Times
Drug tests for THC in the body are generally divided into two categories, historical use and present intoxication. Historical use includes the infamous urine drug test along with the hair follicle test.
These tests almost always target the THC-COOH molecule, a non-psychoactive substance that has absolutely nothing to do with a person’s level of sobriety; used only to determine if someone used the substance in the past, regardless if use was during personal time.
To detect present intoxication, the blood serum or saliva test is typically employed. These tests indicate whether or not active THC molecules are present, therefore being an indicator of impairment, despite a persons level of tolerance (note: marijuana is not alcohol, therefore marijuana tolerance is not comparable to alcohol tolerance).
These type of tests are supposed to be accurate to within a couple of days but for blood tests, this is under heavy scrutiny. For instance, it can literally take a week for a healthy, chronic marijuana user’s THC levels to drop below 5 ng/mL of blood, which is the national standard for blood tests.
Below is a breakdown and general length of detection time for each testing method through which THC metabolites can be detected.
Table: Marijuana Use and Approximate Detection Times
Urinalysis Drug Testing
This is the most common drug test. The test is quite easy and all that is required is a sample of urine by the subject for the test to be carried out. The sample is first taken to the laboratory and screened under a threshold sensitivity level (immunoassay). If the targeted THC-COOH metabolites of the test are found to be below the national standard of 50 ng/mL, then the sample is marked negative, you pass the test, and typically, no further action is taken.
However, if you fail the immunoassay by going above 50 ng/mL, then the sample is marked positive and tested a second time for confirmation.
The second test for confirmation is conducted with the use of more advanced equipment. A Gas Chromatography/Mass Spectrometer (GC/MS) is used. This test is analyzed under a threshold of 15 ng/ml, which very accurate and extremely stereoselective (meaning that it knows exactly what it’s looking for and can distinguish between two closely related molecules). If the sample is higher than 15 ng/ml, then a “Test Positive for Marijuana/Cannabis” is reported.
If you are a chronic marijuana user, THC can be detected in your system using a urine test for up to 12 weeks depending on the quantity as well as frequency of use. For a light user with average measurements, the general rule of two weeks to 30 days may be used. If you just used marijuana once and stopped, the odds of passing a test within the first week are decent (around 50%).
However, in all cases, the odds of testing positive for up to 30 days will always be there, depending on many factors. The weight of body fat a person has, for example, plays a major role in our calculations. There are literally hundreds, if not thousands, of drug test submissions where people have used cannabis once and still failed 30+ days later.
Hair Follicle Drug Testing
Although hair testing is more accurate compared to the other tests, it is relatively expensive and not reliable if a person only used marijuana once in the past. However, the advantage this test has over all others is that it can be used to detect the use of marijuana for months.
Just an inch of hair from a person’s scalp is all specialists need for the test. And hair from any other part of the body can still be used – the pubic area, arms and legs.
Blood Serum Drug Testing
This type of test is used to detect current usage of drugs such as marijuana. It also helps to investigate car/work accidents. After a single use of marijuana, the blood test can produce positive results for 6-24 hours. However, for regular users, a blood test can produce positive results for up to 7 days or more.
Below is an illustration of how long it can take a chronic user to pass a blood and urine test after stopping the use of cannabis. User measurements are as follows: 31 year old male, 170 lbs with a 29 inch waist, multiple dabs per day plus high potency flower for more than three months before going cold turkey for this study. In addition, the user had a very fast metabolic speed with a high level of cardio exercise.
Although this is just one scenario based on one chronic user, what this demonstrates, in many cases, is that THC detection within the blood can remain for almost as long as it’s detectable in the urine. For explanation on why this is the case, we need to look a little closer at what is being tested.
Saliva Drug Testing
This is the newest test for marijuana usage and hence not commonly used. Usually, it is used to investigate car and work accidents. This is because the test can detect whether a person is under the influence of marijuana or not. A saliva test can produce positive results within the first 24 hours of its usage.
How Long Does Marijuana & Cannabis Stay in Your System (World’s #1 Resource) In an effort to provide the most accurate answer for how long marijuana stays in your system , we set up a simple