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Neuroscience For Kids


Marijuana is one of the world's most commonly used illegal drugs. There are approximately 300 million users worldwide and 28 million users in the United States (Diaz, 1997). Marijuana comes from a plant called "Cannabis sativa." The chemical in this plant that produces the altered states of consciousness is called "delta-9 tetrahydrocannabinol" or "THC." Marijuana is usually smoked like a cigarette, but it can also be cooked into baked goods like brownies or cookies or brewed like a tea. THC is also contained in "hashish" (hash) which is the resin from the marijuana plants. Hash is usually smoked in a pipe. Other names for marijuana include: grass, pot, reefer and weed.

Effects of Marijuana on the Nervous System

THC acts on cannabinoid receptors which are found on neurons in many places in the brain. These brain areas are involved in memory (the hippocampus), concentration (cerebral cortex), perception (sensory portions of the cerebral cortex) and movement (the cerebellum, substantia nigra, globus pallidus). When THC activates cannabinoid receptors, it interfers with the normal functioning of these brain areas. In low to medium doses, marijuana causes:

In high doses, marijuana can cause:

Scientists have known for a long time that THC interacted with cannabinoid receptors in the brain, but did not know why the brain would have such receptors. They thought that the brain must make some kind of substance that naturally acted on these receptors. In 1992, they found the answer...anandamide. Anandamide is the brain's own THC (just like "endorphin" is the brain's own morphine). Still, scientists are not sure what the function of anandamide is in the normal brain.

The effects of marijuana start as soon as 1-10 minutes after it is taken and can last 3 to 4 hours or even longer. Experiments have shown that THC can affect two neurotransmitters: norepinephrine and dopamine. Serotonin and GABA levels may also be altered.

Whether marijuana can produce addiction is controversial. Also controversial is whether marijuana causes long-term mental abnormalities. Only future research will give us the answers. It is interesting to note that there are NO documented cases of a fatal overdose produced by marijuana. However, because there is a high level of tar and other chemicals in marijuana, smoking it is similar to smoking cigarettes. The lungs get a big dose of chemicals that increase the chances of lung problems and cancer later in life.

How long does THC stay in your body and for how long can it be detected after you use marijuana?

The amount of time depends on several factors such as how much a person has smoked, how long a person has smoked for, and the method used to detect THC or its metabolites. Marijuana can be detected in urine, blood and saliva using methods called thin layer chromatography, high pressure liquid chromatography, gas chromatography, enzyme immunoassay and radioimmunoassay. The most psychoactive ingredient in marijuana is delta-9-tetrahydrocannabinol (THC). THC is broken down into several other compounds that are also psychoactive. The half-life of THC is about 24 hours. However, the metabolites of THC can be detected for 45 to 60 days after the last use.

According to Maistro et al., in the book Drug Use and Misuse (1991):

"Approximately half of the THC is excreted over several days, and the remainder by the end of about a week. However, some metabolites of the THC, a number of which may still be active in the system, can be detected in the body at least thirty days following ingestion of a single dose and, following chronic use, in the urine for several weeks."

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Take a short on-line, interactive quiz about amphetamines, cocaine and marijuana.

For more information about marijuana, see:

  1. Marijuana Detection Windows
  2. Diaz, J. How Drugs Influence Behavior. A Neuro-Behavioral Approach, Upper Saddle River (NJ): Prentice Hall, 1997.
  3. Marijuana: Facts for Teens - from the National Institute on Drug Abuse
  4. Marijuana: Facts for Parents - from the National Institute on Drug Abuse
  5. Marijuana Update from the National Institute on Drug Abuse.
  6. Is CBD Oil Legal?

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