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How Long Does Marijuana Stay in Your System?

  • Medical Author: Divya Jacob, Pharm. D.
  • Medical Editor: Dr. Pallavi Suyog Uttekar, MD

What is marijuana?

Marijuana, also known as weed, pot, or ganja, is a medicinal plant of the Cannabis family. It contains a psychoactive compound known as tetrahydrocannabinol (THC) that has major intoxicating effects. The leaves, seeds, stems, or roots, are mainly used for intoxication purposes. Marijuana preparations are usually smoked in pipes, joints, or water pipes (bongs). Marijuana users also add it to food or brew it as a tea. Marijuana is the most abused substance in the United States. Approximately, 11.8 million young adults used marijuana in 2018.

What happens when you smoke marijuana?

Marijuana, when inhaled, exhibits short- and long-term effects on the brain.

Short-term effects

  • After smoking marijuana, THC passes from the lungs into the bloodstream, and it is carried to the brain and other organs. The effect is generally felt after 30 minutes to one hour. THC activates parts of the brain, which produce the primary psychoactive and the intoxication effects. Other effects felt are:
    • Altered senses
    • Distorted sense of time
    • Mood swings
    • Impaired memory
    • Hallucinations
    • Delusions
    • Psychosis (disconnected from reality)
    • Impaired coordination
    • Fear
    • Anxiety
    • Difficulty in thinking clearly
    • Increased appetite

Long-term effects result in some permanent changes to the brain, such as losing mental abilities and functioning.

Other physical changes are:

  • Breathing problems
  • Increased heart rate
  • Problems with child development during and after pregnancy
  • Intense nausea and vomiting

How long does marijuana/weed stay in your system?

Detectable amounts of THC may remain in the body for days or even weeks after use. Upon consumption of marijuana, THC is absorbed and stored by various body tissues and organs. The drug is primarily broken down by the liver. The by-products formed by the breakdown are immediately cleared via urine. However, THC stored in the body tissue gets continuously released back into the bloodstream over time, where it continues to be broken down by the liver and cleared in urine until all of it is depleted from the body. In a chronic user, the excretion rate of THC through urine is less, so it builds up in the liver.

When will marijuana show up on a drug test?

Several tests are used to detect the presence of marijuana. They include:

  • Saliva test: A person can test positive for marijuana for up to 34 to 48 hours after the last marijuana use.
  • Urine test: Infrequent users test positive for one to three days, moderate users can test positive for 7 to 21 days and a heavy user can test positive for a month or longer after the last marijuana use.
  • Hair test: Marijuana can be detected in a hair test for up to 90 days.
  • Blood test: Marijuana will be visible in a blood test for up to 36 hours.

What are the treatments for marijuana abuse and addiction?

Marijuana addiction is mostly treated in a rehabilitation center. Behavioral therapies that are effective in treating marijuana addiction are:

  • Motivational enhancement therapy (MET): Motivates the individual to give up a marijuana addiction.
  • Cognitive-behavioral therapy (CBT): Teaches the user to stop using the drugs and ways to avoid or manage other problems.
  • Contingency management (CM): Involves exchanging vouchers as a reward for not taking drugs.

Although medications may not be effective in treating addictions, some antidepressant medications may help with managing withdrawal symptoms and preventing relapses.

Marijuana, also known as weed, pot or ganja, is a medicinal plant of the Cannabis family. It contains a psychoactive compound known as tetrahydrocannabinol (THC). THC activates parts of the brain, which produce the primary psychoactive and the intoxication effects.

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.