NIDA for Teens: The Science Behind Drug Abuse
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What Are the Short-Term Effects of Marijuana Use?

For some people, smoking marijuana makes them feel good. Within minutes of inhaling, a user begins to feel “high,” or filled with pleasant sensations. THC triggers brain cells to release the chemical dopamine. Dopamine creates good feelings—for a short time. But that’s just one effect…

Imagine this: You're in a ball game, playing out in left field. An easy fly ball comes your way, and you're psyched. When that ball lands in your glove your team will win, and you'll be a hero. But, you're a little off. The ball grazes your glove and hits the dirt. So much for your dreams of glory.

Such loss of coordination can be caused by smoking marijuana. And that's just one of its many negative effects. Marijuana affects memory, judgment, and perception. Under the influence of marijuana, you could fail to remember things you just learned, watch your grade point average drop, or crash a car.

Also, since marijuana can affect judgment and decision making, using it can cause you to do things you might not do when you are thinking straight—such as engaging in risky sexual behavior, which can result in exposure to sexually transmitted diseases, like HIV, the virus that causes AIDS, or getting in a car with someone who’s been drinking or is high on marijuana.

It’s also difficult to know how marijuana will affect a specific person at any given time, because its effects vary based on individual factors: a person’s genetics, whether they’ve used marijuana or any other drugs before, and how much marijuana is taken. Effects can also be unpredictable when marijuana is used in combination with other drugs.

THC Affects Brain Functioning

THC is up to no good in the brain. THC finds brain cells, or neurons, with specific kinds of receptors called cannabinoid receptors and binds to them.

Certain parts of the brain have high concentrations of cannabinoid receptors. These areas are the hippocampus, the cerebellum, the basal ganglia, and the cerebral cortex. The functions that these brain areas control are the ones most affected by marijuana.

For example, THC interferes with learning and memory—that is because the hippocampus—a part of the brain with a funny name and a big job—plays a critical role in certain types of learning. Disrupting its normal functioning can lead to problems studying, learning new things, and recalling recent events. The difficulty can be a lot more serious than forgetting if you took out the trash this morning, which happens to everyone once in a while. A recent study followed people from age 13 to 38 and found that those who used marijuana a lot in their teens and continued into adulthood had a significant drop in IQ, even if they quit.

Smoking Marijuana Can Make Driving Dangerous

The cerebellum is the section of our brain that controls balance and coordination. When THC affects the cerebellum’s function, it makes scoring a goal in soccer or hitting a home run pretty tough. THC also affects the basal ganglia, another part of the brain that’s involved in movement control.

These THC effects can cause disaster on the road. Research shows that drivers on marijuana have slower reaction times, impaired judgment, and problems responding to signals and sounds. A recent analysis of data from several studies found that marijuana use more than doubles a driver’s risk of being in an accident. In fact, studies conducted in a number of localities have found that approximately 4 to 14 percent of drivers who sustained injury or death in traffic accidents tested positive for THC.

Marijuana Use Increases Heart Rate

Within a few minutes after inhaling marijuana smoke, an individual's heart begins beating more rapidly, the bronchial passages relax and become enlarged, and blood vessels in the eyes expand, making the eyes look red. The heart rate, normally 70 to 80 beats per minute, may increase by 20 to 50 beats per minute or, in some cases, even double. This effect can be greater if other drugs are taken with marijuana.