How Long Does Marijuana Stay in Your Hair? – THC (Tetrahydrocannabinol), the psychoactive chemical in marijuana, can stay in the body for days or weeks. Hair follicle tests are the most sensitive tests, as they can detect THC for up to 90 days after the last use.
Of note, these tests are examining the oil in skin that transfers to hair, so they occasionally may show a false positive. Moreover, a person who comes into regular contact with a THC user could, in theory, test positive on a hair follicle test.
The length of time THC remains in the body or continues to be detectable on a drug test depends on several factors besides the test that is being administered. For example, how much and how often marijuana is ingested, as well as a person’s body fat content, can affect this duration.
Some substances, such as alcohol, can be entirely eliminated from the body in just a few hours. However, marijuana is fat-soluble rather than water-soluble, meaning that it is stored in fatty tissues for long periods.
Drug tests can identify THC in urine, blood, and hair for several days after use. Saliva tests can detect the presence of THC for only a few hours.
Detection Windows
Marijuana can stay in the body from 3-30 days, sometimes longer. Research on the length of time a test can identify marijuana revealed a broad range. A study from 2017 suggested a detection window for a single marijuana cigarette of around 72 hours.
The same study noted that detection windows differ and will depend on how often a person ingests marijuana.
Findings included the following:
- For a person smoking marijuana for the first time, tests may identify it for around three days.
- For a person who smokes marijuana 3-4 times per week, the detection window is 5-7 days.
- For a person who smokes marijuana daily, tests may detect it for 30 days or longer.
Detection windows also depend on the type of test conducted. Estimates for marijuana tests are as follows:
- Urine tests can identify marijuana for between 3–30 days after use
- Saliva tests can detect marijuana for up to 24 hours after use, sometimes longer
- Blood tests can only detect THC for 72 hours after use
How much marijuana do you have to ingest to fail a drug test?
Most drug tests can detect relatively small amounts of THC, and the amount of THC in a given dose of marijuana can vary. Some research has examined precisely how much a person must smoke to fail a drug test.
A 2012 study looked at marijuana users smoking a single joint at 6.8 percent THC. Urine concentrations of THC were highest between 0.6-7.4 hours after smoking. Using a urine test, scientists detected metabolites of THC in the urine of 100% of frequent users. Occasional users also had metabolites identified, but not always as many. The study concludes that “THCCOOH, THC-glucuronide, and THCCOOH-glucuronide were measurable in all frequent smokers’ urine and 60%, 100%, and 100% of occasional smokers’ urine samples, respectively.”
A 2017 study reports on testing with hair samples from 136 marijuana users claiming no use, light use, or heavy use. Researchers cut hair into 1 cm sections to test for exposure of up to 30 days prior. The results of 77% of heavy users and 39% of light users came back positive. No non-users produced positive results, indicating that false positives in hair tests are rare.
7 Factors That Affect Detection Time
Several factors influence if a test identifies the presence of marijuana, including the following:
1. Sensitivity
More sensitive tests can detect lower amounts of THC.
2. THC Dose
Marijuana drug tests check for THC, not marijuana itself. Moreover, the amount of THC that a person ingests is the most significant factor.
The effects of THC are collective, meaning that a person who smokes several times in a brief period has consumed a higher dose of THC than a person who smokes once. Therefore, they are more likely to receive positive test results.
The potency of each dose of THC is also a factor. However, how high a person feels is not a reliable measure. Other factors, such as the consumption of other drugs or alcohol, can intensify this feeling as well as other effects.
3. Body Fat Percentage
Because marijuana has a strong affinity to fat, people with higher body fat levels may break down cannabis at a slower rate than a leaner person. Body mass index (BMI) is a method one can use to estimate body fat. However, because weight increases with muscle mass, BMI is not always an ideal way to measure body fat.
4. Sex
Typically, women have more body fat than men. For this reason, women may metabolize marijuana at a slower rate.
5. Hydration Levels
Dehydration raises concentrations of THC in the body. While drinking lots of water is not likely to affect a drug test in any meaningful way, being severely dehydrated might.
6. Exercise
Exercise is not thought to significantly alter the rate at which the body breaks down THC, but engaging in exercise right before a drug test may make an impact.
A small study of fourteen regular marijuana users examined the effects of 35 minutes of exercise on a stationary bike. The results found that THC concentrations increased significantly, suggesting that exercising right before a drug test may increase the chances of testing positive. Researchers posit that exercise may prompt fat cells to release THC. In fact, people with higher BMIs in the study had more notable increases in THC.
7. Metabolism
For a drug test to have negative results, the body must rid THC from the system, as well as metabolites that are associated with THC. People with faster metabolisms will likely eliminate THC more rapidly than those with slower metabolisms.
Again, dehydration can also increase the likelihood of testing positive. Moreover, proper hydration affects metabolism, and can prevent a drug test from revealing unusually high levels of THC. For those whose test results border on positive and negative, this could mean that being dehydrated may increase the likelihood of positive result.
Unfortunately, there is no reliable way to speed up a person’s rate of metabolism. Exercise might help the body break down more THC, but, as we have discussed, exercising too close to a test may also produce a positive result.
In the end, the most influential factors are the time from the last exposure to the time of testing and the type of test being administered.
Do you need treatment for Marijuana Abuse?
If you are afraid of failing a drug test and have been unable to quit using marijuana, you may want to consider seeking professional help. Marijuana use can be habit-forming, and some people find it challenging to stop using when they want to.
Our center specializes in the outpatient treatment of drug abuse and alcohol. We are also equipped to treat co-occurring mental health conditions and provide emotional and social support. We offer therapeutic services, such as psychotherapy and counseling, that are intended to help people find the root causes of their drug abuse or addiction.
If you are struggling with marijuana abuse, contact us today! Discover how we help people break the cycle of addiction for life!