- Urine and blood screens are the most common tests for marijuana
- Blood tests measure THC levels while urine tests measure THC-COOH levels
- THC is broken down by the liver into THC-COOH and other metabolites
- Heavy users may test positive for up to 4-6 weeks after last intake
- Infrequent users should be clear after 1-2 days
- The amount of time it takes to clear a drug test varies greatly from user to user
TruthOnPot.com – All marijuana users are faced with a common problem when they are asked to undergo a drug test. The issue is that marijuana can be detected in the body for days or even weeks after last being used.
How long it stays in your system depends on how frequently you use marijuana as well as your body’s rate of metabolism.
Urine vs Blood Tests
Urine tests are the most common way of testing for marijuana, but blood tests have been used as well, especially when driving under the influence is suspected. Blood tests measure levels of active THC and therefore can only detect recent marijuana use.
On the other hand, urine tests measure levels of THC metabolites – the compounds that result from the breakdown of THC – such as THC-COOH. THC metabolites are known to remain in the body for much longer and therefore pose more risk to users being tested.
A study published in 2007 by National Institute on Drug Abuse (NIDA) researchers summarizes the findings of previous research on the absorption and elimination of THC associated with marijuana use.
THC From Smoking Marijuana
Smoking is the most common way of using marijuana and also happens to be the fastest method of absorbing THC.
THC has been found to be immediately detectable after the first inhale of marijuana smoke, with blood levels of THC reaching a peak at around 9.0 min into smoking – just under a minute before the patients took their last puff (9.8 min).
While patients seem to control their individual doses by varying how deeply they inhale, the average amount of THC in the blood dropped to 60% of the peak at 15 min after the last inhale and to 20% at 30 min. By the 2 hour mark, THC levels were below 5 ng/ml.
It took between 3 to 12 hours for THC to drop below detection limits (0.5 ng/ml) for the low-dose group and from 6 to 27 hours for the high-dose group of the study. However, the subjects of the study were not regular marijuana smokers, which explains why THC levels fell so quickly.
THC From Oral Ingestion of Marijuana
A less common form of consuming marijuana is by oral ingestion. Oral ingestion of THC leads to a very different pattern of THC levels. A study involving patients given 20mg THC cookies found the peak in blood levels of THC to occur between 1 to 5 hours following consumption. Another study conducted by Kim and Yoon (1996) using 10 mg THC capsules of Marinol identified a peak between 1 to 2 hours following ingestion.
In studies involving hemp oils and dronabinol, THC blood levels were found to fall below detection limits (0.5 ng/ml) by 25 hours following intake. On the other hand, THC-COOH was still measurable for more than 50 hours after the last dose.
THC blood concentrations decrease rapidly after you finish smoking due to its fast distribution into tissues and metabolism in the liver. THC is a fat-soluble molecule and is initially absorbed by organs with high blood circulation, such as the lung, heart, brain and liver.
THC and its metabolites are usually retained by organs of the body for much longer than it remains in the blood. Studies show that THC is mostly stored in fat tissues and – with regular use – can stay there for up to 4 weeks.
THC Metabolism and Elimination
THC is primarily metabolized by the liver, but other tissues such as the brain, intestine and lungs may contribute as well. Studies show that within 5 days – 80 to 90% of THC is eliminated from the body – mostly in the form of its metabolites. More than 65% is excreted in feces and 20% in urine.
On the other hand, a study found that THC could remain above the limit of detection (0.3 ng/ml) in the blood of regular users for up to a month following cessation, although it varies by individual.
THC in Urine
THC is not found in its active form in urine samples, but rather as the metabolite THC-COOH. The results of urine tests have also been shown to vary greatly from user to user, even in controlled laboratory settings.
For new or infrequent users, the window of time for detection (50ng/ml limit) is believed to last 1 to 2 days.
On the other hand, studies have shown that regular users can test positive (20 ng/ml limit) for THC metabolites for up to 46 consecutive days following marijuana usage. In an extreme case, a heavy cannabis user of more than 10 years was able to test positive (20 ng/ml limit) for up to 67 days after last being exposed to marijuana.
How Long Will I Test Positive For?
Based on these findings, it is impossible to say for sure how long marijuana will remain in your system for. There are a number of factors that contribute to this uncertainty, such as the level of THC dose, method of intake, duration and frequency of use and your body’s metabolism rate. On top of all that, various drug tests have different levels of accuracy and cut-off limits.
As studies have shown, the chances of testing positive for marijuana – even after a break in use – are much higher if you happen to be a regular user as opposed to someone who has just smoked once or twice in the past few weeks.