When a person smokes marijuana, THC quickly passes from the lungs into the bloodstream. The blood carries the chemical to the brain and other organs throughout the body. The body absorbs THC more slowly when the person eats or drinks it. In that case, they generally feel the effects after 30 minutes to 1 hour.
THC acts on specific brain cell receptors that ordinarily react to natural THC-like chemicals. These natural chemicals play a role in normal brain development and function.
Marijuana over activates parts of the brain that contain the highest number of these receptors. This causes the “high” that people feel. Other effects include:
- altered senses (for example, seeing brighter colors)
- altered sense of time
- changes in mood
- impaired body movement
- difficulty with thinking and problem-solving
- impaired memory
- hallucinations (when taken in high doses)
- delusions (when taken in high doses)
- psychosis (risk is highest with regular use of high potency marijuana)
Marijuana also affects brain development. When people begin using marijuana as teenagers, the drug may impair thinking, memory, and learning functions and affect how the brain builds connections between the areas necessary for these functions. Researchers are still studying how long marijuana’s effects last and whether some changes may be permanent.
For example, a study from New Zealand conducted in part by researchers at Duke University showed that people who started smoking marijuana heavily in their teens and had an ongoing marijuana use disorder lost an average of 8 IQ points between ages 13 and 38. The lost mental abilities didn’t fully return in those who quit marijuana as adults. Those who started smoking marijuana as adults didn’t show notable IQ declines.5
In another recent study on twins, those who used marijuana showed a significant decline in general knowledge and in verbal ability (equivalent to 4 IQ points) between the preteen years and early adulthood, but no predictable difference was found between twins when one used marijuana and the other didn’t. This suggests that the IQ decline in marijuana users may be caused by something other than marijuana, such as shared familial factors (e.g., genetics, family environment).6 NIDA’s Adolescent Brain Cognitive Development (ABCD) study, a major longitudinal study, is tracking a large sample of young Americans from late childhood to early adulthood to help clarify how and to what extent marijuana and other substances, alone and in combination, affect adolescent brain development.
Is marijuana a gateway drug?
Use of alcohol, tobacco, and marijuana are likely to come before use of other drugs. Animal studies have shown that early exposure to addictive substances, including THC, may change how the brain responds to other drugs. For example, when rodents are repeatedly exposed to THC when they’re young, they later show an enhanced response to other addictive substances—such as morphine or nicotine—in the areas of the brain that control reward, and they’re more likely to show addiction-like behaviors.
Although these findings support the idea of marijuana as a “gateway drug,” the majority of people who use marijuana don’t go on to use other “harder” drugs. It’s also important to note that other factors besides biological mechanisms, such as a person’s social environment, are also critical in a person’s risk for drug use and addiction.
This is a 2-part urine test to look for delta-9-tetrahydrocannabinol, or THC. THC is the active ingredient in marijuana. The test can find out if THC or related chemicals from marijuana called metabolites are in your urine. The test is considered quite accurate. You may have to do the urine test in a healthcare provider’s office or with a technician present.
Why do I need this test?
You may need this test as a requirement before being hired for a job. You might also have this test if you are showing signs of drug abuse. Your healthcare provider may also give you this test to monitor drug abuse treatment and to quickly look for any signs of relapse. Regular testing may help you recover from drug abuse more successfully.
What other tests might I have along with this test?
Your healthcare provider may also order tests on samples of your hair, saliva, sweat, or blood.
What do my test results mean?
Test results may vary depending on your age, gender, health history, the method used for the test, and other things. Your test results may not mean you have a problem. Ask your healthcare provider what your test results mean for you.
A positive result can mean recent and past marijuana use. The urine marijuana test will be positive if the amount of THC in the sample is more than 50 nanograms per milliliter (ng/mL). If you use marijuana but your test is negative, it could be because your THC levels are below this level. A confirmation test can be done by a more sensitive method if the screening test is positive. Confirmation tests are done to be certain that the original test result is a true result. It is done to make sure the result was not caused by a medicine or other substance affecting the test.
Urine tests can’t show the exact day or hour that marijuana was last used. This is because THC can stay in your system even after you’ve stopped using marijuana. THC can linger on average up to 10 days for a casual user. It stays in your system for 2 to 4 weeks if you use marijuana often, and more than a month if you use it more often.
How is this test done?
This test needs a urine sample. You may need to give the sample with a medical staff member or technician in the room.
Does this test pose any risks?
This test poses no known risks. But the results may affect your job or legal standing.
What might affect my test results?
Medicines used to treat nausea from chemotherapy, such as dronabinol, give positive test results. Cannabidiol (CBD) found in a medicine used to treat seizures and some herbal supplements may also give positive results. CBD comes from the marijuana plant and may have some THC. Tell your healthcare provider if you’ve been taking these medicines. You may be asked to give proof you have been prescribed the medicine.