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Home Physiology How long does THC stay in your system?
Dec 5, 2019 Updated on Jul 21, 2021 7 min read

How long does THC stay in your system?

author
by Philip Ghezelbash
Medically reviewed by Codi Peterson, PharmD
Drug testing

THC can stay in your system for several weeks, but how long exactly depends on a range of factors such as frequency of use, your individual metabolic rate, and body fat percentage. That said, THC detection times rarely exceed 30 days, according to a 2005 fact-sheet written by Paul Cary, director of the Toxicology and Drug Monitoring Laboratory at the University of Missouri.

Tetrahydrocannabinol, or THC, the most notable of the active chemicals found in cannabis that is responsible for the plant’s well-known psychoactive effects, is fat soluble. Because of its preference for fats, THC finds its way into the fatty tissues of the body, where it is stored and slowly excreted. It’s this fat storage results in THC’s long detection window. 

The method with which one consumes cannabis also affects which metabolic pathway THC follows in the body. That isn’t relevant only for the time it takes your body to excrete it, but also the time it takes for it to be metabolized and begin to affect you.

For instance, when cannabis is vaped or smoked, it’s quickly absorbed by the lungs and there is a sharp increase of THC in the bloodstream within minutes. The major effects of inhalation tend to last a few hours. 

When cannabis is ingested, on the other hand, the THC enters the bloodstream through the intestinal walls, is sent to and processed by the liver, and only then can it go to the brain, where it causes the high. Typically the psychoactive effects of THC that is orally consumed can be felt within an hour, while peak effects occur before four hours, and the overall experience can last as long as eight hours, sometimes longer. The psychoactive effects of edibles also tend to be felt more intensely due to the production  of 11-hydroxy-THC (the active metabolite of THC).

How long a THC high lasts and how long THC stays in your system are two very different things. There are some claims of “cannabis hangovers,” with anecdotal reports of lingering fatigue following cannabis use. However, in general, when the primary psychoactive effects of cannabis (ie. the high) are over, things return to normal, despite lingering THC metabolites being released from fat cells for several days or weeks.

Young man laying on a couch smoking a joint
Have you ever experienced a “cannabis hangover?” (Shutterstock)

Everyone metabolizes THC differently

After THC is consumed, it is quickly broken down by the body and turned into molecules called metabolites. Within about six hours of smoking cannabis, cannabis metabolites can be detected in the urine.1 More than 100 different THC metabolites2 have been identified and their half-lives differ greatly — some metabolites can be cleared by the body quickly while others can be stored in fat tissue and detectable in urine for days,weeks, or even months. 

One study published in the Journal of Analytical Toxicology examined THC concentrations in the urine of Norweigan prisoners. With these tests, scientists were able to estimate the initial half-life of THC is around 1.3 days for frequent and infrequent users. This means that within 4-7 days, the vast majority of the THC will be gone from the system. In frequent users, however, a slower excretion occurs and is reflected by a 10-day terminal half-life. The researchers found that they could detect THC  in the urine of frequent users for up to 2-4 weeks after quitting.  

The wide ranges presented are because there are numerous factors that determine how long THC stays in your system.

  • Metabolism: Every individual has a unique metabolic rate that is dependent on numerous factors including age, activity levels, diet, genetics, concurrent medications, and health conditions. In general, a faster metabolism results in a more rapid metabolization and excretion of THC.
  • Body fat: Since THC metabolites are stored in fat tissue, people with a higher body fat percentage will naturally store higher amounts of cannabinoids. The result is more THC lingering in the body and a longer THC detection window. 
  • Gender: Women have higher body fat percentages than men on average, and therefore it may take them modestly longer than men to clear THC from their bodies.
  • Hydration: Staying hydrated does not help to clear cannabinoids more quickly, even if the internet claims it does. Dehydration does however result in more concentrated THC metabolites in urine, which may affect THC detection through urine drug screening. 

Because of all of the factors involved, there may not be a way to accurately predict how long THC will remain detectable. There is, however, enough clinical research out there that one could draw general estimates to determine — how long does weed stay in your system.

Methods of testing for THC

According to a 2004 review published in the Therapeutic Drug Monitoring journal, “detection time is longest in hair, followed by urine, sweat, oral fluid, and blood.”3

BloodUrineHairSaliva
Single use36 hrs72 hrsProbably undetectable12 hours
Moderate use7 days14 days90 days2 days
Chronic use30 days30+ days90 days28 days
NotesDetection window can vary highly depending on type of test cutoff level, metabolites screened, etc.4, 5Detection beyond 30 days is uncommon but has been reported, especially in heavy use and in those with excessive body fat.6The detection window is extremely long. The reason 90 days is the standard window testing facilities are looked at, but can vary from individual based on hair growth and based on laboratory procedures.7The smallest detection window of all testing types. Still, detection times vary depending on consumption method and test type. Smoking cannabis increases the likelihood of a positive saliva test due to mouth contamination.8

How long does THC stay in your hair follicles?

After entering and circulating through the body, some THC will reach hair follicles through small blood vessels where small amounts are deposited into the growing hair. Once the THC is in the hair, it will likely be detectable for years. In fact, hair preserves drug residues so well that scientists can even find evidence of cocaine use in the hair of a 900 year old mummy.9 But, fear not–that is not the normal detection window. Hair follicle drug tests can assess previous drug use for up to 90 days, because as standard they only test the newest 3.9cm of hair. Since human hair usually grows 1.5gm each month, the detection window is estimated to be about 3 months. The tests are often geared for detecting a level of cannabis use equivalent to 1 or 2 joints per month. 

How long does THC stay in your urine?

Urine testing is by far the most common type of THC testing. Tests can vary in their sensitivity so it’s hard to make generalizations, but according to Mayo Clinic Proceedings,10 the primary THC metabolite can be detected in urine for the following lengths of time: 

  • Single use: 3 days 
  • Moderate use (four times per week): 5-7 days
  • Chronic use (daily): 10-15 days
  • Chronic heavy use: Over 30 days

How long is THC detectable in your sweat?

Sweat testing is a non-invasive cannabis testing method that has not yet, so don’t expect to get this test yet, but it could be useful for applications in the future. In one study, THC elimination was evaluated in 11 daily cannabis users after stopping cannabis use. Sweat patches were worn for seven days, and were analyzed for THC. Eight out of the 11 subjects had negative results after the second week.11

Female jogger taking a break
Sweat testing is considered to be a non-invasive cannabis testing method (Shutterstock)

How long is THC detectable in your saliva?

Cannabis is also detectable in saliva. According to a 2014 review on cannabinoids in oral fluid, cannabis can be detected in saliva for the following time periods: 

  • Occasional cannabis users: ~2 days
  • Chronic daily cannabis smokers:  ~14 days, but can be up to 28 days days

How long does THC stay in your blood?

Similar to other cannabis testing methods, the period of THC metabolite detectability in the blood is dependent on the frequency of use. According to a review published in the Therapeutic Drug Monitoring Journal, in general, THC is detectable in the blood for one to two days.12


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Other research has shown slightly longer THC blood detectability for heavy cannabis users. In a 2009 study, published in the journal Addiction, researchers tested THC blood concentrations in 25 heavy cannabis users for seven days of abstinence. Six out of 25 users had a positive test after 7 days of abstinence. Of note, this test was looking directly at THC, not the THC metabolite (THC-COOH) most commonly looked for and that lingers in the body longer.13

Implications for drug testing

Millions of employees and potential employees are drug tested every year in the United States and elsewhere. They are measured for drug metabolites in their urine, blood, hair, saliva, breath, sweat, and even fingernails. 

There are countless methods of detoxing available, with few being based on much science. These range from drinking cranberry juice to taking laxatives and other herbal supplements. Many people attempting to fool test results frequently increase the amount of water they drink in order to “flush out” THC. The reasoning behind this approach is that over-hydrating oneself decreases the concentration of THC metabolites in the urine, thus decreasing the chance of a positive result. Individuals using this over-hydration method also often take a vitamin B-12 supplement to turn their urine more yellow, making it appear less dilute. 

Excessive exercise in an attempt to burn fat, since THC is stored in fat, is not unheard of either. In theory this is a logical approach, but ironically, a study published in the journal Drug & Alcohol Dependence showed that exercise can release stored THC metabolites into the bloodstream, which could actually increase the odds of testing positive.  The bottom line is that there is no way to guarantee a negative test result for THC, but an understanding of the detection windows may help you better plan your next job change. 

Sources

  1. Spindle TR, Cone EJ, Schlienz NJ, et al. Urinary Excretion Profile of 11-Nor-9-Carboxy-Δ9-Tetrahydrocannabinol (THCCOOH) Following Smoked and Vaporized Cannabis Administration in Infrequent Cannabis Users. J Anal Toxicol. 2020;44(1):1-14. doi:10.1093/jat/bkz038
  2. Gonçalves J, Rosado T, Soares S, et al. Cannabis and Its Secondary Metabolites: Their Use as Therapeutic Drugs, Toxicological Aspects, and Analytical Determination. Medicines (Basel). 2019;6(1):31. Published 2019 Feb 23. doi:10.3390/medicines6010031
  3.  Verstraete A. G. (2004). Detection times of drugs of abuse in blood, urine, and oral fluid. Therapeutic drug monitoring, 26(2), 200–205. https://doi.org/10.1097/00007691-200404000-00020
  4. Lee D, Huestis MA. Current knowledge on cannabinoids in oral fluid. Drug Test Anal. 2014;6(1-2):88-111. doi:10.1002/dta.1514
  5. Karschner EL, Swortwood MJ, Hirvonen J, et al. Extended plasma cannabinoid excretion in chronic frequent cannabis smokers during sustained abstinence and correlation with psychomotor performance. Drug Test Anal. 2016;8(7):682-689. doi:10.1002/dta.1825
  6. Verstraete A. G. (2004). Detection times of drugs of abuse in blood, urine, and oral fluid. Therapeutic drug monitoring, 26(2), 200–205. https://doi.org/10.1097/00007691-200404000-00020
  7. Moeller KE, Kissack JC, Atayee RS, Lee KC. Clinical Interpretation of Urine Drug Tests: What Clinicians Need to Know About Urine Drug Screens. Mayo Clin Proc. 2017;92(5):774-796. doi:10.1016/j.mayocp.2016.12.007
  8. Lee D, Huestis MA. Current knowledge on cannabinoids in oral fluid. Drug Test Anal. 2014;6(1-2):88-111. doi:10.1002/dta.1514
  9. Huestis MA, Gustafson RA, Moolchan ET, et al. Cannabinoid concentrations in hair from documented cannabis users. Forensic Sci Int. 2007;169(2-3):129-136. doi:10.1016/j.forsciint.2006.08.005
  10. Moeller KE, Kissack JC, Atayee RS, Lee KC. Clinical Interpretation of Urine Drug Tests: What Clinicians Need to Know About Urine Drug Screens. Mayo Clin Proc. 2017;92(5):774-796. doi:10.1016/j.mayocp.2016.12.007
  11. Huestis MA, Scheidweiler KB, Saito T, et al. Excretion of Delta9-tetrahydrocannabinol in sweat. Forensic Sci Int. 2008;174(2-3):173-177. doi:10.1016/j.forsciint.2007.04.002
  12. Verstraete A, . Detection Times of Drugs of Abuse in Blood, Urine, and Oral Fluid. Therapeutic Drug Monitoring. 2004; 26 (2): 200-205.
  13. Karschner EL, Schwilke EW, Lowe RH, et al. Do Delta9-tetrahydrocannabinol concentrations indicate recent use in chronic cannabis users?. Addiction. 2009;104(12):2041-2048. doi:10.1111/j.1360-0443.2009.02705.x

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