Fraser Horton
Fraser Horton
Last Updated on August 7, 2021

THC (tetrahydrocannabinol) and CBD (cannabidiol) are the two major cannabinoids found in weed which are responsible for many of its recreational and medical properties. Shortly after consuming weed in whichever form, they bind to the cannabinoid receptors, which are a part of the endocannabinoid system in the body, and modify their action, in that way producing the unique effects that cannabis is known for.

Whatever the frequency of your cannabis use, you must already know that weed stays in your body for much longer after the effects subside. This is the natural pathway of the cannabinoids through the body and knowing what takes place and how long it takes for them to get eliminated might be helpful if you’re preparing to take a drug test or want to try detoxing.

Therefore, in this article, we’ll talk about the half-life of THC, or how long it takes for it to get eliminated from the body, as well as the factors that can influence the elimination.

How Does THC Move Through the Body When You Consume Cannabis?

THC (full name delta9-tetrahydrocannabinol or delta9-thc) is the psychoactive compound found in the cannabis plant. It’s the main cannabinoid responsible for producing the euphoric and relaxing effects, also known as “the high,” but it also has some medicinal properties. 

In order to understand the half-life of THC and how long it stays in the body, we need to learn about the pharmacokinetics of THC, or in other words, how THC moves through the body from the moment of absorption to the time when it’s eliminated.

How fast THC will get absorbed in your body depends on the mode of consumption. Typically, inhaling weed will result in a much faster absorption because it will reach your bloodstream directly through your lungs. In fact, it takes only a few seconds for it to become detectable in your blood plasma, and 3-10 minutes to reach peak plasma concentration.

On the other hand, ingesting weed will result in a slower distribution because edibles need to be digested first. In this case, THC will reach a peak concentration in the blood plasma within 1 or 2 hours after ingestion. 

How THC Gets Metabolized

THC is a lipophilic or fat-soluble compound, which means that it binds to lipids (fat). Due to this, THC will slowly start to move from the blood plasma into the fatty tissues in the body, including the liver, lungs, and spleen. Depending on the method of consumption, it can take at least 10 hours for THC to clear from the blood plasma completely.

In the liver, THC gets broken down into byproducts also known as metabolites. This is done by the cytochrome P450 (CYP) system which is a superfamily of enzymes responsible for metabolizing not only THC, but also other drugs and medications. About 80%-90% of THC gets metabolized in the liver and further broken down into other compounds, while the rest leaves the body unchanged.

First, It Gets Converted Into an Active Metabolite

First, THC gets converted into a metabolite called 11-OH-THC (full name 11-hydroxy-delta-9-tetrahydrocannabinol or 11-hydroxy-THC) which is an active metabolite and produces similar effects as THC, only a little milder. This metabolite is more abundant when weed is ingested, which is why the high from edibles lasts longer. 11-OH-THC is the predominant metabolite found in feces. 

Then, It Gets Further Broken Down Into an Inactive Metabolite

Further, 11-OH-THC is deactivated and converted into another metabolite called THC-COOH (full name 11-nor-delta-9-tetrahydrocannabinol-9-carboxylic acid 11-nor-9-carboxy-THC). This metabolite is inactive and it’s what most drug tests look for because it stays the longest in the body. THC-COOH is more prevalent in urine, hence the popularity of urine drug tests.

From here, the THC metabolites travel back into the bloodstream and get distributed in the body fat for a prolonged period of time. Over time, they gradually get eliminated from the body through fecal and urinary excretion. 

What Is the Half-Life of THC?

Half-life is a term that refers to the period of time required for half of the quantity of a substance to get eliminated from the body. Knowing the elimination half-life of THC-COOH, as the most stubborn metabolite, can help you gauge how much time it takes for it to be fully eliminated.

However, you should also know that the half-life of THC isn’t a constant value and depends on many things. Since THC gets broken down into different byproducts which get stored in different parts of the body, all of these compounds will have slightly varying half-lives.

Overall, THC gets eliminated the fastest from blood and oral fluids (in a matter of hours), while it takes the longest to be eliminated from urine (days and often weeks), because the metabolites linger for longer, especially for frequent marijuana users.

Variables That Can Influence THC Half-Life

For cannabis users, there are many factors that can influence the pace at which THC and its metabolites will get eliminated from the body and some of them can be subject to changes.

Frequency of Marijuana Use

The frequency of use is one of the biggest factors that can influence how long THC will stay in the body. Since THC metabolites get stored in body cells for a prolonged period of time, this also would mean that for frequent users the metabolites will accumulate after each use. Therefore, it will take much longer for them to get eliminated compared to infrequent users.

Dosage

Similarly, the dosage also plays a major part. Low doses will get metabolized and cleared from the body much faster than high doses, and this applies especially to medical marijuana users who may need a higher dose to treat their symptoms.

Which Strain You Use

Marijuana has so many good-sounding strains that sometimes it can be hard to choose which one to try. Apart from the usual cannabis Indicas and cannabis Sativas, there are hybrids that are even more diverse and potent. But whichever strain you choose, it’s the THC levels that matter. The higher the THC levels, the more metabolites you will end up storing.

Your Metabolism

Your metabolism can also have a big impact not only on the half-life of THC, but also on the way your body will metabolize it. Your THC tolerance also matters as some marijuana users are more sensitive to the effects of THC than others. That being said, some individuals have naturally higher metabolisms and will clear THC metabolites faster than others.

Body Mass Index (BMI)

The body mass index refers to the percentage of body fat. Since metabolites get predominantly stored in fat cells, it’s believed that people with a higher BMI will store the metabolites for longer, but there can be exceptions depending on the person.

THC and Drug Testing – How Do Drug Tests Detect the Presence of THC?

Most drug tests look for the inactive metabolite THC-COOH which can be found in urine and in the hair shaft. The blood test and the oral fluid (saliva) test are the only ones that look for the THC concentrations in the blood and saliva.

Drug tests, also called immunoassays, have cutoff levels that detect the concentration of THC or its metabolites. The cutoff levels are different for each test and any value at or above that number will indicate a positive result.

The samples are tested twice, with the second time being confirmatory using testing methods such as gas chromatography/mass spectrometry (GC/MS) or liquid chromatography/tandem mass spectrometry (LC/MS/MS) to rule out any false positives from the initial testing.

Drug Tests Detection Windows

Additionally, each drug test has a different detection time depending on how long THC or its metabolites stay in a certain part of the body. The blood test and the oral fluid tests have the shortest detection times because they don’t look for the metabolites but the parent drug. They are most commonly used to detect current impairment or very recent use, up to 72 hours.

Urine tests can go further in time because they look for the THC-COOH metabolite. Depending on the frequency of use, they can detect THC in the urine sample from 4 to 40 days after usage, and even 70 days for chronic users.

Hair drug tests have the longest detection window because they can detect THC-COOH 90 days after use. This happens because THC metabolites get deposited in the hair shaft which makes them detectable. Hair drug tests are used to detect habitual drug use since they go back further in time. Heavy users will most likely have the largest amounts of THC deposits in their hair.

Conclusion – A Lot Goes Into the Half-Life of THC 

When you consume weed, THC goes through a long process of metabolization and elimination. It gets converted into a number of metabolites that get stored in the fatty tissues of your body for a prolonged period of time. Your frequency of use of cannabis is one of the factors that will largely determine what the half-life of THC will be for your body. Another factor is the dosage and strain which can vary from user to user. 

Additionally, there are four different types of drug tests that have different detection times, ranging from 72 hours to 90 days after last use. They also have different assay methods where some look for THC itself, and others look for THC metabolites.

Additional Sources

Huestis MA (2007). Human cannabinoid pharmacokinetics. Chemistry & biodiversity, 4(8), 1770–1804. https://doi.org/10.1002/cbdv.200790152

Lucas, C. J., Galettis, P., & Schneider, J. (2018). The pharmacokinetics and the pharmacodynamics of cannabinoids. British journal of clinical pharmacology, 84(11), 2477–2482. https://doi.org/10.1111/bcp.13710

Sharma, P., Murthy, P., & Bharath, M. M. (2012). Chemistry, metabolism, and toxicology of cannabis: clinical implications. Iranian journal of psychiatry, 7(4), 149–156.

Schwilke, E. W., Schwope, D. M., Karschner, E. L., Lowe, R. H., Darwin, W. D., Kelly, D. L., Goodwin, R. S., Gorelick, D. A., & Huestis, M. A. (2009). Delta9-tetrahydrocannabinol (THC), 11-hydroxy-THC, and 11-nor-9-carboxy-THC plasma pharmacokinetics during and after continuous high-dose oral THC. Clinical chemistry, 55(12), 2180–2189. https://doi.org/10.1373/clinchem.2008.122119

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