What Is It?
Marijuana is a mixture of the dried and shredded leaves, stems, seeds, and flowers of the cannabis sativa plant. The mixture can be green, brown, or gray.
A bunch of leaves seem harmless, right? But think again. Marijuana has a chemical in it called delta-9-tetrahydrocannabinol, better known as THC. A lot of other chemicals are found in marijuana, too—about 400 of them, many of which could affect on your health. But THC is the main psychoactive ingredient.  In fact, marijuana’s strength or potency is related to the amount of THC it contains. The THC content of marijuana has been increasing since the 1970s. For the year 2007, estimates from confiscated marijuana indicated about 8 percent THC on average.
What Are the Common Street Names?
There are many slang terms for marijuana that vary from city to city and from neighborhood to neighborhood. Some common names are: “pot,” “grass,” “herb,” “weed,” “Mary Jane,” “reefer,” “skunk,” “boom,” “gangster,” “kif,” “chronic,” and “ganja.” 
How Is It Used?
Marijuana is used in many ways. The most common method is smoking loose marijuana rolled into a cigarette called a “joint” or “nail.” Some users brew it as tea or mix it with food. Others smoke “blunts”-cigars hollowed out and filled with the drug. And sometimes marijuana is smoked through a water pipe called a “bong.”
What Are the Common Effects?
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.
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 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. Some people may suffer sudden feelings of anxiety and have paranoid thoughts—which is more likely to happen when higher doses are used or when it is taken orally. The problem is that it’s difficult to tell what the effects of marijuana will be for any given person at any time, because they vary based on the person, their drug history, how much marijuana is taken, and its potency. Effects can also be unpredictable when other drugs are mixed with marijuana.
Also, since marijuana can affect judgment and decision making, using it can lead to risky sexual behavior, resulting in exposure to sexually transmitted diseases, like HIV, the virus that causes AIDS.
What Are the Short-Term Effects of Marijuana Use?
- problems with memory and learning
- distorted perception
- difficulty thinking and solving problems
- impaired coordination
- increased heart rate
THC Impacts 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, to which it binds.
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.
Do these effects persist? We don’t know for sure in humans, but studies in rats show that exposure to THC for a long period of time can damage neurons in the hippocampus. So, is it really worth the risk?
Smoking Marijuana Can Make Driving Dangerous
The cerebellum is the section of our brain that does most of the work on 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 highway. Research shows that drivers on marijuana have slow reaction times, impaired judgment, and problems responding to signals and sounds on the road. 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 delta-9-tetrahydrocannabinol (THC), the active ingredient in marijuana.
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.
What Are the Long-Term Health Effects of Marijuana Use?
The list of negative effects from using marijuana goes on and on. Here are a few examples:
Some studies show that when people have smoked large amounts of marijuana for years, the drug harms mental functions. Heavy or daily use of marijuana affects the parts of the brain that control memory, attention, and learning. A working short-term memory is needed to learn and perform tasks that call for more than one or two steps. Long-term users report less life satisfaction, poorer education and job achievement, and more interpersonal and mental health problems compared to non-users.
Marijuana also may affect your mental health. Studies show that early use can increase the risk of developing psychosis [a severe mental disorder in which there is a loss of contact with reality, including false ideas about what is happening (delusions) and seeing or hearing things that aren’t there (hallucinations)] in adulthood in individuals having a genetic or other vulnerability to the disease. Also, rates of marijuana use are often higher in people with symptoms of depression or anxiety—but which came first can be difficult to determine, and whether they are causally related is not yet known.
Lungs and airways
People who abuse marijuana are at risk of injuring their lungs through exposure to respiratory irritants and carcinogens found in marijuana smoke. The smoke from marijuana contains some of the same substances found in tobacco smoke; plus, marijuana users tend to inhale more deeply and hold their breath longer, so more smoke enters the lungs.  Not surprisingly, marijuana smokers have some of the same breathing problems as tobacco smokers—they are more susceptible to chest colds, coughs, and bronchitis than nonsmokers. However, whether marijuana use increases the risk for lung and other cancers is not yet determined.
Most people don’t think of marijuana as addictive—they are wrong. Marijuana increases dopamine, and once that happens, a user may feel the urge to smoke marijuana again, and again, and again. Repeated use could lead to addiction—a disease where people continue to do something, even when there are severe negative consequences involved, like when their relationships at home, school, work, or with friends suffer. In 2006, the majority of youth (age 17 or younger) entering drug abuse treatment reported marijuana as their primary drug abused.
Marijuana users can also experience a withdrawal syndrome when they stop using the drug. It is similar to what happens to tobacco smokers when they quit—people report being irritable, having sleep problems, and weight loss—effects which can last for several days to a week after drug use is stopped. Relapse is common during this period, as users also crave the drug to relieve these symptoms.
Does Marijuana Lead to the Use of Other Drugs?
While most marijuana smokers do not go on to use other drugs, long-term studies of high school students and their patterns of drug use show that few young people use other illegal drugs without first trying marijuana. For example, the risk of using cocaine is much greater for those who have tried marijuana than for those who have never tried it. Using marijuana puts children and teens in contact with people who are users and sellers of other drugs. So, a marijuana user may be more likely to be exposed to and urged to try other drugs. The effects of marijuana on the brain of adolescents—still a work in progress—may also affect their likelihood of using other drugs as they get older. Animal studies suggest this to be true, but it is not yet demonstrated in people.