Marijuana—also known as weed, pot, grass, bud, herb, ganja and mary jane, among other slang terms—refers to the dried leaves, flowers, stems, and seeds of the Cannabis sativa plant, which contains the psychoactive (mind-altering) chemical delta-9-tetrahydrocannabinol (THC) as well as other related compounds. Cannabis plant material can also be concentrated in a resin called hashish or a sticky black liquid called hash oil.
Marijuana is the most commonly used illicit drug in the United States, typically smoked as a hand-rolled cigarette (joint) or in a pipe or water pipe (bong). The drug is also smoked in what’s called a blunt—a cigar that’s been emptied of tobacco and refilled with a mixture of marijuana and tobacco. Marijuana smoke has a pungent and distinctive sweet-and-sour odor.
Another way of ingesting the drug is to mix the plant’s leaves, flowers, stems or seeds into food or to brew the leaves as a tea.
Some varieties of cannabis plants are also known as hemp, although "hemp" more commonly refers to a fiber derived from such plants. Historically, hemp fiber has been used to make rope, paper, fabrics and sail canvas. Today, hemp fiber is used to create concrete-like blocks for construction projects, bioplastics, jewelry and biofuels. In colonial America, hemp production was required by English rule. George Washington grew it as a crop at Mount Vernon. At that time, hemp plants were low in tetrahydrocannabinol (THC), the active component of cannabis, and crops were valued for their role in industry.
Use of medicinal cannabis began in America in the 1850s, when products with cannabis extracts were produced and sold to treat maladies such as pain and muscle spasm. Soon after, pharmaceutical regulations were introduced in some states. Products containing habit-forming substances such as cannabis were often labeled as poisons and, in some cases, were available only with a physician’s prescription.
Today, marijuana is classified by the federal government as a Schedule I substance, which means the drug presents a high risk for abuse and is deemed to have no medicinal uses. However, several states have legalized marijuana for adult recreational use, and 23 states as well as the District of Columbia allow use of medical marijuana to treat certain medical conditions.
While many have called for the legalization of marijuana to treat pain and nausea caused by HIV/AIDS, cancer, and other conditions, clinical evidence does not show that the therapeutic benefits of medical cannabis or medical marijuana outweigh the health risks. To be considered a legitimate medicine by the U.S. Food and Drug Administration (FDA), a drug must have well-defined and measurable ingredients consistent from one unit (such as a pill or injection) to the next. Since the cannabis plant contains hundreds of chemical compounds that vary from plant to plant (and those various compounds may cause different effects) and because the drug is typically ingested via smoking, its medicinal use is difficult to evaluate.
At this time, several THC-based drugs have been approved by the FDA to treat pain and nausea. And scientists continue to investigate the medicinal properties of other chemicals found in the cannabis plant, such as cannabidiol, a non-psychoactive compound being studied for its effectiveness in treating pain, pediatric epilepsy and other conditions.
It’s also important to note that marijuana potency has increased significantly over the years. In 2012, the THC concentration in marijuana samples confiscated by law enforcement averaged near 15 percent, compared with an average concentration of four percent in the 1980s. High-potency forms of the drug can expose new users to increased concentrations of THC and greater risk of experiencing adverse or unpredictable reactions. For frequent users, higher potency can increase the risk of marijuana addiction.
Learn more about the history of marijuana and legislative policy.
When marijuana is smoked, THC passes rapidly from the lungs into the bloodstream, which carries the substance to the brain and other organs throughout the body. THC is absorbed more slowly when ingested through food or drink.
Regardless of how THC is ingested, the substance acts specifically on the brain cell’s cannabinoid receptors. These receptors—ordinarily activated by THC-like chemicals produced naturally by the body—are part of the neural communication network, called the endocannabinoid system, which plays an important role in normal brain development and function.
The highest density of cannabinoid receptors is found in parts of the brain that influence pleasure, memory, thinking, concentration, sensory and time perception, and coordinated movement. Marijuana over-activates the endocannabinoid system, causing the "high" and other effects that users experience, such as:
Research indicates that using marijuana can cause or exacerbate problems in daily life. Heavy users tend to report lower life satisfaction, poorer mental and physical health, more relationship problems and less academic or career success when compared with non-using peers. Use of the drug is also associated with a higher likelihood of dropping out of school. Several workplace studies associate marijuana use with increased absences, tardiness, accidents, workers' compensation claims and job turnover.
Marijuana use is associated with a range of health issues, particularly related to heart and lung problems and mental health conditions.
Marijuana smoke is an irritant to the lungs, and frequent smokers can experience many of the same respiratory problems experienced by tobacco smokers, such as:
One study found that people who smoke marijuana frequently but do not smoke tobacco have more health problems and miss more days of work than those who don't smoke marijuana, mainly due to respiratory illnesses. It is not yet known whether marijuana smoking contributes to the risk for lung cancer.
Research also indicates that use raises the heart rate by 20-100 percent shortly after smoking; this effect can last up to three hours. One study found that marijuana smokers have a 4.8-fold increase in the risk of heart attack in the first hour after using the substance. The risk may be even greater for older adults and those with cardiac vulnerabilities.
A number of studies link chronic marijuana use and mental illness. High doses can produce a temporary psychotic reaction in some users. Use of the drug can also worsen the course of illness for patients who have schizophrenia. A series of large, longitudinal studies also shows a link between marijuana and the development of psychosis.
Marijuana abuse has also been associated with other mental health problems, such as:
More research is needed to better understand these mental health links and ramifications.
Using marijuana during pregnancy is associated with increased risk of neurobehavioral problems in babies. Because THC and other compounds mimic the body's own endocannabinoid chemicals, marijuana use by pregnant mothers may alter the developing endocannabinoid system in the brain of the fetus. Consequences for the child can include difficulties related to attention, memory and problem solving.
Marijuana has also been shown to negatively affect the brain development of young people who are heavy users. The effects on thinking and memory may last a long time or even be permanent. A study of individuals who began using the drug in adolescence revealed substantially reduced connectivity in areas of the brain responsible for learning and memory. A long-term study in New Zealand showed that people who began smoking the drug heavily in their teens lost an average of eight points in IQ between ages 13-38. The lost cognitive abilities were not fully restored in those who quit smoking marijuana as adults. Those who started smoking the drug in adulthood did not show significant IQ declines.
Additionally, because it impairs judgment and motor coordination, marijuana use contributes to a greater risk of injury or death while driving a car. Data analysis suggests that marijuana use more than doubles a driver's risk of being in an accident. On a related note, the combination of marijuana and alcohol increases driving impairment more than either substance alone.
Contrary to common belief, marijuana is an addictive substance. Research suggests that approximately nine percent of users develop addiction. The estimated incidence of addiction increases among those who start using at a young age (an estimated 17 percent develop addiction) and among people who use the drug daily (an estimated 25-50 percent become addicted).
Individuals who are addicted to cannabis may experience symptoms of withdrawal when attempting to stop using the drug. Long-term users who try to quit report withdrawal symptoms such as irritability, sleeplessness, decreased appetite, anxiety and drug craving--all of which can make it difficult to abstain. Behavioral interventions, including cognitive-behavioral therapy and motivational incentives (e.g., providing vouchers for goods or services to patients who remain abstinent) have proven effective in treatment and rehab for marijuana addiction. Although medications to address marijuana/cannabis addiction are not currently available, recent discoveries about the endocannabinoid system offer promise in developing medications to ease withdrawal symptoms, block the drug's intoxicating effects, and prevent relapse.
Addiction to marijuana is most commonly diagnosed during adolescence or young adulthood. However, recent trends toward greater societal acceptance of marijuana use and increased availability of both recreational and medical forms of the drug may increase the addiction rate in older adults. As with other types of drug addiction, there are behavioral and physical signs that can signal marijuana addiction (known medically as cannabis use disorder).
Behavioral changes include:
Other signs of marijuana abuse, misuse and addiction include:
Long-term drug abuse is associated with a number symptoms of marijuana withdrawal, which typically develop within one week of discontinuing use. Some of the most common symptoms of cannabis withdrawal include:
Since many of these withdrawal symptoms mimic warning signs of other conditions and problems, an expert assessment by an addiction professional is necessary to determine whether marijuana withdrawal is the cause.
Treatment options or "rehab" for marijuana addiction is similar to treatment programs and protocols for addiction to alcohol and other drugs. Evidence-based therapies such as Twelve Step facilitation, cognitive-behavioral therapy, motivational enhancement therapy and other scientifically valid approaches can be effective addiction treatment options, depending on the individual's situation, other drug abuse, and treatment needs. Learn more about our treatment options.
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