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THC Half-Life in Urine, Saliva, Blood, Sweat, and Hair

Half-life is a scientific term that stands for a period of time required for half of some entity or substance to go through a specified process. In drug pharmacology, for example, a drug’s half-life is the time needed for the elimination or breakdown of half of that drug’s active elements. (1)

THC half-life is important for marijuana smokers because it determines how long this substance will stay in their systems. Drug tests typically screen for the presence of THC or its metabolites in the tested material. Therefore, by understanding their half-lives in various bodily substances, we can better understand how to pass a drug test.

Table of Contents

THC half-life

How Is THC Excreted from the Body?

About 80%–90% of THC is metabolised in the liver and leaves the body in the form of hydroxylated and carboxylated metabolites. Only 10%–20% of THC is excreted unchanged. (2)

The main hydroxylated metabolite is 11-hydroxy-THC (11-OH-THC), which is the prevalent metabolite in feces. (2) The primary carboxylated metabolite is 11-nor-delta-9-tetrahydrocannabinol-9-carboxylic acid (THC-COOH), which is the predominant metabolite in urine and the target substance in urine drug testing. (3) More than 65% of THC and its metabolites is excreted in feces and about 20% in urine. (2)

The full elimination of THC and all its metabolites from the body takes several weeks. (4)

Different THC Half-Lives

THC half-life is not a single and constant value. Once THC enters the body, most of it turns into metabolites, which are distributed to various tissues and can be detected in blood, saliva, sweat, urine, and hair. All metabolites, as well as THC itself, have different half-lives in each of these materials. Moreover, these values vary for every person, depending on his/her metabolism. Even the route of administration affects the half-life. So, there is no simple and exact answer for questions about THC half-life.

Half-Life of THC in Urine

Since THC-COOH is the prevalent metabolite excreted in urine, checking it is most advisable for detecting cannabis use, so all urine tests for marijuana look for THC-COOH, not THC itself.

No significant difference has been found in the rate of its urinary excretion in frequent and infrequent users, but half-life of THC-COOH in urine in the first days is different compared with a later period. For example, one study found it to be 30 hours in the first 7 days and 44–60 hours in the first 12 days after cannabis consumtion. (2)

This is consistent with another study that determined the urinary excretion half-life of THC-COOH in infrequent users as 1.3 days within the first 5 days following intake and 1.4 days for frequent users. (5) Nevertheless, starting from day 5 up to day 16, the average half-life of THC-COOH was 3.9 days. (5)

Some heavy marijuana users with slow metabolism were found to excrete THC metabolites much more slowly than others and have unusually long THC-COOH half-life. For them, the median half-life was 7.1 days after 5 days of abstinence, with a maximum of 10.3 days. (5)

Another study found that THC-COOH concentrations in urine of marijuana smokers drop rapidly only until they reach a level of 20–50 ng/ml. After that they continue to drop much more slowly. (6)

You can use the THC calculator based on the half-life of THC-COOH to calculate its approximate level in urine for each day.

Half-Life of THC in Saliva

In saliva drug testing, the parent unchanged THC is screened. The study found that the smoked dose and the history of cannabis use have significant influence on THC concentrations in saliva only right after smoking. After 15 minutes, the effect is minimal. (7)

The THC elimination half-life in oral fluids has been found to be near 1.5 hours after smoking both low and high doses of marijuana (7) and for both occasional and chronic smokers. (8)

Half-Life of THC in Blood

The half-life of THC in blood is highly dependent on the route of administration (whether oral or intravenous) and, unfortunately, is not accurately measured at the present time.

Different studies report very different half-lives for cases where THC is consumed by smoking the cannabis plant. One study in 1998 found that for delta 1-tetrahydrocannabinol in plasma the elimination half-life was almost 4 days. (9)

Another study (10) recorded the following elimination half-lives in blood plasma:

  • THC: 25–36 hours
  • 11-OH-THC: 12–36 hours
  • THC-COOH: 25–55 hours

In the most recent study (11) from 2007, the following elimination half-lives in serum were reported:

  • THC: 1.4 hours
  • THC-OH: 2.0 hours
  • THCA: 3.4 hours

Half-Life of THC in Sweat

Though no single research offers reliable findings on the half-life of THC in sweat, daily smokers of marijuana have been found to have positive results on sweat patch testing in the first week after they stopped smoking. In subsequent weeks, the sweat tests came out negative. (12) Knowing that urine drug tests for daily smokers have similar results, we can assume that the half life of delta-9-tetrahydrocannabinol (THC) in sweat is close to the half life of THC-COOH in urine.

Half-Life of THC in Hair

Though there is no available research about this value, traces of THC are detectable in the hair follicle test about 3 months after the last cannabis use. (13) This shows that the half-life of THC in hair is much longer as compared with all the aforementioned half-lives.

How to Reduce THC Half-Life in Your Body

As was said before, people with different metabolism have different half-lives of THC in their bodies, which means that accelerating metabolism will help reduce this period of time in your body and get rid of THC much faster.

If you want to decrease the half-life of THC in your system, you must increase the rate at which it is eliminated from your body. This can be achieved by the following:

  • Exercising—releases THC molecules from the body’s fat tissues.
  • Consuming a fiber-rich diet—promotes better bowel movement thereby facilitating faster fecal excretion of THC.
  • Drinking more fluids—will lead to frequent urination and increase urinary excretion of THC.
  • THC detox drinks—are fortified with ingredients (herbs, vitamins, and minerals) that have natural detox properties.


  1. https://whatis.techtarget.com/definition/half-life
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3570572/
  3. https://www.cdc.gov/mmwr/preview/mmwrhtml/00000138.htm
  4. https://www.ncbi.nlm.nih.gov/pubmed/18847571
  5. https://academic.oup.com/jat/article-pdf/23/5/323/2328939/23-5-323.pdf
  6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2689518/
  7. https://www.ncbi.nlm.nih.gov/pubmed/17579974/
  8. https://www.ncbi.nlm.nih.gov/pubmed/20465868
  9. https://www.ncbi.nlm.nih.gov/pubmed/2899638
  10. https://www.researchgate.net/publication/10846458_Grotenhermen_F_Pharmacokinetics_and_pharmacodynamics_of_cannabinoids_Clin_Pharmacokinet_42_327-360
  11. https://pdfs.semanticscholar.org/2826/8e9f66c3bd27571caeb4585bd424b1e9ab2f.pdf
  12. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2277330/
  13. https://www.sciencedirect.com/science/article/pii/S2090536X13000774