The Scientific Reason Why THC Stays in Your System

The primary reason why anyone is concerned about THC-metabolites remaining in the body is due to a potential impending drug screening. As cannabis legalization spreads across North America, some employers are finally practicing common sense. These companies realize that a growing number of people use weed.

It is the world’s most popular ‘illicit’ recreational drug. This is why some companies no longer fire or refuse to hire people based on a positive screening for marijuana.

Yet in California, and other states where the herb is recreationally legal, firms can still fire people for using the substance. It doesn’t matter if you use it on a day off. If you test positive for cannabis, your employer could terminate your contract.

Approximately 12% of Americans use cannabis. However, an estimated 94 million have used it at least once in their lifetime.

This helps explain why there is such a market for THC detox drinks. Such products claim they can quickly remove the cannabinoid from your system. Crucially, this process could help you pass a urinalysis and keep your job. At least, this is the theory. In practice, it is difficult to determine the efficacy of such drinks. Read more in this guide to THC detox.

In many cases, they involve drinking a ton of water along with the product. At that stage, you don’t know if it is the drink or the excess water helping! Such items usually include fiber to help remove THC via your fecal matter. Yet there isn’t the same market for detox drinks designed to quickly remove cocaine, amphetamines, and other illegal drugs from the system.

Why? It is because THC remains in your system a lot longer than most other illegal drugs. We investigate the reasons in this article.

How Long Does THC & Other Drugs Remain in the Body?

For marijuana users, the humble urinalysis is their most feared enemy. It is one of the cheapest and easiest drug screenings for companies to administer. More importantly, it enables them to detect THC-metabolites (THC-COOH) for a more extended period than blood or saliva tests.

The body produces THC-COOH when the liver breaks down THC. It isn’t a bad thing physiologically speaking, but it does ensure the metabolite remains in your system longer.

A lot depends on your frequency of use as well. Some reports claim that chronic users could have remnants of THC in their system for 11 weeks after they stop using weed! This is when they submit to a urinalysis. In general, an infrequent user who takes a blood test could test negative within 2-3 days. In contrast, a urine test could detect THC-COOH for up to seven days in certain circumstances.

why thc stay in your system

For regular users, a blood test may detect THC-COOH for 1-2 weeks. However, with a urine test, you are looking at 3+ weeks. The period extends to 6+ weeks if you are a chronic user! For other drugs, it is a different tale.

The following are approximate detection times for casual users when submitting to a urine test:

  • Cocaine: 1-3 days
  • Heroin & Opiates: 1-4 days
  • Amphetamines: 1-3 days
  • PCP: 3-7 days
  • LSD: 8 hours
  • Ecstasy: Up to 2 days
  • Methadone: 2-3 days
  • Morphine: 1-2 days

It seems as if cannabis users are getting a bum deal! But why is this the case?

Why Does Marijuana Remain in the System for So Long?

There is a myriad of reasons. Relevant factors include things like:

  • Rate of cannabis consumption
  • Metabolism
  • Age
  • Gender
  • Body size/weight
  • General health

What most people don’t realize is that THC (and its metabolites) are fat-soluble. It can remain in the body’s fat cells for literally months at a time. Follicle tests are also a nightmare because THC-metabolites can stay there for several weeks after use.

But why does it stay in our system for so long, you ask? You have to remember that urine tests don’t detect THC itself. Instead, they find THC-COOH, a non-intoxicating metabolite. It can linger in the body for days, weeks, or even months without impairing the individual. This is one of the reasons why a considerable proportion of positive drug tests involve marijuana.

Fat cells usually aren’t something you burn quickly. How many of us exercise? Or even drink enough water? Probably not many of us. If we are not burning the fat where THC metabolites are stored, they will stick around for a long time.

If you are a regular user, the chances of getting THC out of your system within a couple of days is very slim. This is even the case if you exercise regularly. You can drink lots of water to try to flush it out of your system. However, if you are smoking weed regularly, your body’s fat cells contain copious amounts of THC metabolites.

Urine Testing Results in Practice

The following should help provide a visual illustration of how long THC metabolites stay in your system.

urine testing results in practice

The data from Subjects B, E, and G comes from Huestis et al., published in the Journal of Analytical Toxicology in October 1992. The Oral Dose data comes from Law et al., from the same publication in May 1984. This is old information, but it does paint a troubling picture for cannabis users.

Subjects B, E, and G all received a single dose of a standard NIDA marijuana cigarette. They were all monitored for urine levels of THC-COOH at regular intervals. After two days, subjects B and G still tested above the 50ng/ml threshold for a urinalysis. Subject E never exceeded the level despite taking the same amount of THC. The above helps highlight the fluctuations in testing.

Things are even worse if you consume a standard Oral Dose, as seen by the subject with that name in the graph. This individual received a 20mg THC dose. Incredibly, they tested above 50ng/ml for SIX days!

urine testing results in practice

The above chart features data from a Huestis et al. study, published in the Journal of Analytical Toxicology in October 1996. It highlights the time taken for THC-COOH to reach your urine. As you can see, three of the four subjects didn’t test above 50ng/ml for nearly four hours after using cannabis. The fluctuation is apparent again. Subject G reaches the threshold within two hours. In contrast, Subject E never gets there!

The Issues Faced by Regular Users

If you are a regular marijuana user, it can take a very long time to clear out your system.

the issues faced by regular users

Once again, the data is old, but it is good enough for NORML’s California website! The above graph comes from research by Ellis Jr et al., published in Clinical Pharmacology and Therapeutics in November 1985.

Look at regular user C. They continue to show THC-COOH levels of above 80ng/ml for more than five weeks after their last use. They would fail a test for over five weeks! Oddly enough, regular user B retreats below the cutoff of 50ng/ml within ten days or so.

What Happens with a Urine Drug Test?

The urine test is relatively simple. The process involves urinating into a specimen cup. In general, the test requires at least 45ml of liquid. You leave your belongings in one room and proceed to the toilet. A tester will accompany you to ensure you don’t cheat. Once you are finished, place the lid on the cup and hand it to the administrator. The cup gets sealed, and the tester measures the temperature of the sample.


Your urine gets tested for various drugs and their metabolites. If you have more than 50ng/ml of THC-COOH in your system, you fail the test. Depending on the organization, they may use a mass spectrometry test to confirm the result. The cutoff point here is 15ng/ml.

Quick Fact: Most employee drug tests actually test for the presence of THC-COOH (a metabolite of THC), rather than THC itself.

In many ways, a urinalysis is an extremely unfair test. It doesn’t detect THC. Instead, it finds metabolites that cause no impairment. It is patently ridiculous that someone can get fired for using weed two months ago!

Some companies now use saliva tests. Your mouth absorbs THC when you smoke, and it will remain in your saliva for nearly three days after consumption. Studies show THC is detectable in saliva for up to 34 hours after marijuana use. This is even the case if you practice excellent oral hygiene.

Things That Impact THC Detection Time

In summation then, the duration that THC stays in your system can also depend mainly on the following:

  • Cannabis Potency: A marijuana strain with 30% THC will ensure metabolites remain in your system longer than a 15% THC strain. That is, assuming you consume the same amount of each.
  • Frequency of Consumption: One-time and infrequent users may escape after a few days. However, regular and chronic users could have traces of THC-COOH in the system for months!
  • Metabolism: The faster the metabolism, the shorter the detection time.
  • Body Fat: THC binds to lipids, which include body fat, but are not limited to it. Lean users will get THC out of their systems faster than those with higher levels of fat.
  • Activity Level: If you exercise a lot, you are more likely to have a lower body fat percentage. This means fewer metabolites can store themselves in fat cells. However, don’t assume that you can ‘sweat’ out the THC. A relatively small percentage is excreted via bodily fluids other than urine. Indeed, you get rid of most metabolites through your feces.
  • Testing Used: Urine and follicle tests have a much longer detection window than blood and saliva tests.
  • Your Urine: If you have acidic urine, the detection window is shorter.

Final Thoughts on THC in the System

If you are one of the tens of millions of people who use cannabis, beware of drug screenings! Unfortunately, an enormous number of organizations still perform employment drug tests. Recent estimates suggest that almost 80% of companies drug screen at least some of their employees.

90% of firms include pre-employment testing as part of the application process. Approximately 88% test new hires before their first day at work!

In some states, people who have lost jobs because of these rules have launched successful lawsuits. However, such stories are relatively few and far between. For most people, a positive result for THC-COOH can end their existing contract, or torpedo their chances of getting a job.

If you are applying for a job, or believe your employer will drug test you soon, take note of your cannabis use. Bear in mind that you won’t get much notice before the screening. If you are unable to abstain, you will need to depend on the THC detox drinks you see online. Let’s say they have ‘mixed’ results. Also, the data we showed proves that the outcome of drug screenings varies from one user to the next.

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