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Marijuana: Facts Parents Need to Know

Want to Know More? Some FAQs about Marijuana


What is marijuana?
Are there different kinds?

Marijuana is a green, brown, or gray mixture of dried, shredded leaves, stems, seeds, and flowers of the hemp plant (Cannabis sativa). Cannabis is a term that refers to marijuana and other drugs made from the same plant. Strong forms of cannabis include sinsemilla (sin-seh-me-yah), hashish (“hash” for short), and hash oil. There are many different slang terms for marijuana and, as with other drugs, they change quickly and vary from region to region. But no matter its form or label, all cannabis preparations contain the mind-altering (psychoactive) chemical THC (delta-9-tetrahydrocannabinol). They also contain more than 400 other chemicals.

How is marijuana used?

Most users roll loose marijuana into a cigarette (called a joint) or smoke it in a pipe or a water pipe, sometimes referred to as a bong. Some users mix marijuana into foods, or use it to brew a tea. Another method is to slice open a cigar and replace the tobacco with marijuana, creating what is known as a blunt. Marijuana cigarettes or blunts sometimes are dipped in PCP or mixed with other substances, including crack cocaine.

How many people use marijuana?

Before the 1960s, many Americans had never heard of marijuana, but today it is the most often used illegal drug in the United States. According to a 2012 national survey, more than 111 million Americans over the age of 12 had tried marijuana at least once, and nearly 19 million had used the drug in the month before the survey.

Researchers have found that the use of marijuana and other drugs usually peaks in the late teens and early twenties, and then declines in later years. Therefore, marijuana use among young people remains a natural concern for parents and the focus of continuing research, particularly regarding its impact on brain development, which continues into a person’s early twenties.

NIDA's annual Monitoring the Future survey reports that among students from 8th, 10th, and 12th grades, marijuana use has increased over the past 5 years; this increased use parallels a softening of perceptions about marijuana’s risks. In 2013, 12.7 percent of 8th graders reported marijuana use in the past year, and 7 percent were current (past-month) users. Among 10th graders, 29.8 percent had used marijuana in the past year, and 18 percent were current users. Among 12th graders, past year use remained the same and 22.7 percent were current users.

Since 1975, the Monitoring the Future (MTF) survey has measured drug, alcohol, and cigarette use and related attitudes among adolescent students nationwide. Drug use is measured across three time periods: lifetime, past year, and past month; for some drugs, daily use is also reported. Initially, the survey included 12th graders only, but in 1991 it was expanded to include 8th and 10th graders.

How does marijuana work?

When marijuana is smoked, its effects are felt almost immediately. This is because THC (marijuana's psychoactive ingredient) rapidly reaches every organ in the body, including the brain. The effects of smoked marijuana can last from 1 to 3 hours. If consumed in foods, the effects come on slower and may not last as long.

Marijuana works through THC attaching to specific sites on nerve cells in the brain and in other parts of the body. These sites are called cannabinoid receptors (CBRs) because they were discovered by scientists trying to understand how marijuana, or cannabis, exerts its effects. THC is chemically similar to a class of chemicals that our body produces naturally, called endocannabinoids, and marijuana disrupts the normal function of this system. CBRs are found in brain areas that influence pleasure, memory, thinking, concentration, movement, coordination, appetite, pain, and sensory and time perception. Because of this system’s wide-ranging influence over many critical functions, it is not surprising that marijuana can have multiple effects—not just on the brain, but on a user’s general health as well. Some of these effects are related to acute intoxication while others may accumulate over time to cause more persistent problems, including addiction.

Teenage girl More than 45% of teens have used marijuana before they graduate from high school.

What are marijuana’s short-term effects?

The following are some effects that marijuana use can produce:

Euphoria (high). THC activates the reward system in the same way that nearly all drugs of abuse do: by stimulating brain cells to release the chemical dopamine.

Memory impairment. THC alters how information is processed in the hippocampus, a brain area related to memory; regular use can affect learning skills and academic achievement, including short-term memory and complex tasks requiring concentration.

Adverse mental reactions in some. These include anxiety, fear, distrust, or panic, particularly in new users or those taking it in a strange setting; some may even experience psychosis, which includes hallucinations, delusions, paranoia, and loss of the sense of personal identity.

Physical changes. Users may have red or bloodshot eyes, increased appetite (“the munchies”), increased heart rate, and sleep issues.

What determines how marijuana affects an individual?
How important is marijuana potency?

Like any other drug, marijuana’s effects on an individual depend on a number of factors, including the person’s previous experience with the drug (or other drugs), biology (e.g., genes), gender, how the drug is taken (smoked versus orally), and the drug’s potency. Potency—determined by the amount of THC contained in the marijuana—has received much attention lately because it has been increasing steadily. In 2012, THC concentrations in marijuana averaged 14.5 percent, compared to around 4 percent in the 1980s. Some current strains contain as much as 30 percent THC. This is based on analyses of marijuana samples confiscated by law enforcement agencies.

So what does this actually mean? For a new user, it may mean exposure to higher concentrations of THC, with a greater chance of an adverse or unpredictable reaction. In fact, increases in potency may account for the rise in emergency department visits involving marijuana use. For experienced users, it may mean a greater risk for addiction if they are exposing themselves to high doses on a regular basis. However, the full range of consequences associated with marijuana’s higher potency is not well understood, nor is it known whether marijuana users adjust for the increase in potency by using less.

Teenage girl Marijuana can be addictive. About 1 in 6 people who start smoking in their teens, and 25–50 percent of people who use it every day, become addicted to marijuana.

Does using marijuana lead to other drug use?

Long-term studies of high school students’ patterns of drug use show that most young people who use other drugs have tried marijuana, alcohol, or tobacco first. For example, young people who have used marijuana are at greater risk of using cocaine than are those who have not used marijuana. We also know from animal studies that rats previously administered THC show heightened brain activation not only when further exposed to THC but also when exposed to other drugs such as morphine—a phenomenon called cross-sensitization, which is not unique to marijuana. Researchers are now examining the possibility that exposure to marijuana in adolescence may cause changes in the brain that make a person more vulnerable to subsequent marijuana addiction or to the risk of becoming addicted to other drugs, such as alcohol, opioids, or cocaine.

It is important to point out, however, that research has not fully explained any of these effects, which are complex and likely to involve a combination of biological, social, and psychological factors.

Hand with hospital equipment In 2011, marijuana was reported in over 455,000 emergency department visits in the U.S. Over 13 percent involved people between the ages of 12 and 17.

Does smoking marijuana cause lung cancer?

We do not know yet. Studies have not found an increased risk of lung cancer in marijuana smokers, as compared with nonsmokers. However, marijuana smoke does irritate the lungs and increases the likelihood of other respiratory problems through exposure to carcinogens and other toxins. Repeated exposure to marijuana smoke can lead to daily cough and excess phlegm production, more frequent acute chest illnesses, and a greater risk of lung infections. Marijuana also affects the immune system, although the implications for cancer are unclear. Moreover, many people who smoke marijuana also smoke cigarettes, which do cause cancer, and quitting tobacco can be harder if the person uses marijuana as well.

Chest X-Ray Marijuana users may have many of the same respiratory problems tobacco smokers have, such as chronic cough and more frequent chest colds.

Since marijuana can be addictive, can it produce withdrawal symptoms when someone quits?

Yes. When they stop using the drug, many long-term users experience symptoms that are similar in type and severity to those of nicotine withdrawal—irritability, sleeping difficulties, anxiety, and craving—which often prompt relapse. Withdrawal symptoms peak a few days after use has stopped and dissipate within about 2 weeks. And while these symptoms do not pose an immediate threat to health, they can make it hard for someone to keep from using the drug.

Is "Spice" (or "synthetic marijuana") as harmful as real marijuana?

Yes. Spice, which is sometimes also called K2 or Fake Weed, consists of shredded dried plant materials that have been sprayed with chemicals designed to act on the same brain-cell receptors as THC, but are often much more powerful and unpredictable. Spice products are labeled “not fit for human consumption” and many are now illegal, but their manufacturers are constantly creating new chemical compounds to evade legal restrictions. Their side effects, like the ingredients, often vary, but emergency rooms report large numbers of young people appearing with rapid heart rates, vomiting, agitation, and hallucinations after using these substances.

Are there treatments for people addicted to marijuana?

Currently, no FDA-approved medications exist for treating marijuana addiction, although promising research is under way to find medications for treating withdrawal symptoms and alleviating craving and other subjective effects of marijuana. Behavioral therapies are available and are similar to those used for treating other substance addiction. These include motivational enhancement to engage people in treatment; cognitive behavioral therapies to teach strategies for avoiding drug use and its triggers and for effectively managing stress; and motivational incentives, which provide vouchers or small cash rewards for sustained drug abstinence. Unfortunately, treatment success rates are rather modest, indicating that marijuana addiction, like other addictions, may need a long-term care approach that varies treatment intensity in line with the person’s changing needs over time.

Brain image Marijuana affects the brain and leads to impaired short-term memory, perception, judgment, and motor skills.

What are other risks related to marijuana that my child should be aware of?

Here are a few that you or your child may not have thought about:

  • As with most drugs, marijuana use interferes with judgment, which can mean a greater chance of engaging in risky behaviors and experiencing their negative consequences (such as acquiring a sexually transmitted disease, driving while intoxicated, or riding with someone else who is intoxicated and getting into a car crash).
  • In addition to psychosis, regular marijuana use has been associated with several psychological effects, including depression, anxiety, suicidal thoughts, and personality disturbances. One of the effects most frequently reported is an “amotivational syndrome” characterized by a diminished or lost drive to engage in formerly rewarding activities. Whether this syndrome is a disorder unto itself or is a subtype of depression associated with marijuana use remains controversial, and whether marijuana causes it or is a response to it is still not understood. More research is needed to confirm and better understand these linkages.
  • Marijuana use during pregnancy may harm the developing fetus. Research suggests that babies born to women who used marijuana during their pregnancies may have subtle neurological alterations and, later in childhood, can show diminished problem-solving skills, memory, and attention. However, the fact that pregnant women who use marijuana may also smoke cigarettes or drink alcohol makes it difficult to determine exactly how much of these effects are attributable specifically to marijuana.
Teenager exhaling smoke Regular marijuana use has been associated with several psychological effects, including depression, anxiety, suicidal thoughts, and personality disturbances.

Is marijuana medicine?

There has been much debate about the possible medical use of marijuana for certain conditions, including nausea relief for cancer chemotherapy patients and boosting appetite in people with AIDS. Currently, 20 states have legalized smoked marijuana for medical purposes, but the FDA, which assesses the safety and effectiveness of medications, has not approved marijuana as a medicine. There have not been enough large-scale clinical trials showing that smoked marijuana’s benefits outweigh its many potential health risks in patients with the symptoms it is meant to treat. Also, to be considered a legitimate medicine, a substance must have well-defined and measurable ingredients that are consistent from one unit (such as a pill or injection) to the next. In addition to THC, the marijuana leaf contains over 400 other chemical compounds, which may have different effects in the body and which vary from plant to plant. This makes it difficult to consider its use as a medicine even if some of marijuana’s specific ingredients may offer benefits.

However, THC itself is an FDA-approved medication. Medicines now on the market deliver the benefits of THC without the dangers and unpredictability of smoking marijuana. Scientists continue to investigate the medicinal properties of THC and other cannabinoids to better evaluate and harness their ability to help patients suffering from a broad range of conditions, while avoiding the negative effects of smoked marijuana.

How can I tell if my child has been using marijuana?

Parents should be aware of changes in their child’s behavior, such as carelessness with grooming, mood changes, and deteriorating relationships with family members and friends. In addition, changes in academic performance, skipping classes or missing school, loss of interest in sports or other favorite activities, a change in peer group, changes in eating or sleeping habits, and getting in trouble in school or with the law could all be related to drug use—or may indicate other problems. See the list of specific warning signs for marijuana use below.

Photo of a destroyed car Driving while high can lead to car accidents.
Marijuana has adverse effects on many of the skills required for driving a car.

If your child is using marijuana, he or she might:

  • seem unusually giggly and/or uncoordinated
  • have very red, bloodshot eyes or frequently use eye drops
  • have a hard time remembering things that just happened
  • have drugs or drug paraphernalia, including pipes and rolling papers (perhaps claiming they belong to a friend, if confronted)
  • have strangely smelling clothes or bedroom
  • use incense and other deodorizers
  • wear clothing or jewelry or have posters that promote drug use
  • have unexplained lack of money or a surplus of cash on hand


This page was last updated March 2014