What is Marijuana?
Marijuana is a green or gray mixture of dried, shredded flowers and leaves of the hemp plant Cannabis sativa. There are over 200 slang terms for marijuana including “pot,” “herb,” “weed,” “boom,” “Mary Jane,” “gangster,” and “chronic.” It is usually smoked as a cigarette (called a joint or a nail) or in a pipe or bong. In recent years, marijuana has appeared in blunts, which are cigars that have been emptied of tobacco and refilled with marijuana, often in combination with another drug, such as crack. Some users also mix marijuana into foods or use it to brew tea.
The main active chemical in marijuana is THC (delta-9-tetrahydrocannabinol). In 1988, it was discovered that the membranes of certain nerve cells contain protein receptors that bind THC. Once securely in place, THC kicks off a series of cellular reactions that ultimately lead to the high that users experience when they smoke marijuana. The short term effects of marijuana use include problems with memory and learning; distorted perception; difficulty in thinking and problem-solving; loss of coordination; and increased heart rate, anxiety, and panic attacks.
Scientists have found that whether an individual has positive or negative sensations after smoking marijuana can be influenced by heredity. A recent study demonstrated that identical male twins were more likely than non-identical male twins to report similar responses to marijuana use, indicating a genetic basis for their sensations. Identical twins share all of their genes, and fraternal twins share about half.
Most parents, teachers, and other caregivers readily advise adolescents and teenagers that using marijuana is a decidedly dumb idea – and a variety of researchers have bolstered these words of wisdom by documenting the effect that the drug can have on developing minds.
According to the National Institute on Drug Abuse (NIDA), scientists who have analyzed the impact of long-term exposure to marijuana have discovered levels of brain damage that mirror the devastation inflicted by other commonly abused substances.
A NIDA document entitled InfoFacts: Marijuana described how this takes place: HC acts upon specific sites in the brain, called cannabinoid receptors, kicking off a series of cellular reactions that ultimately lead to the “high” that users experience when they smoke marijuana. Some brain areas have many cannabinoid receptors; others have few or none. The highest density of cannabinoid receptors are found in parts of the brain that influence pleasure, memory, thoughts, concentration, sensory and time perception, and coordinated movement.
Cannabinoid withdrawal in chronically exposed animals leads to an increase in the activation of the stress-response system3 and changes in the activity of nerve cells containing dopamine. Dopamine neurons are involved in the regulation of motivation and reward, and are directly or indirectly affected by all drugs of abuse.
In February 2005, a NIDA study that appeared in the journal Neurology reported that individuals who smoked marijuana experienced altered blood flow in their brains even after abstaining from the drug for as long as a month. The research, which involved 54 marijuana users and 18 control subjects, revealed significantly higher velocity of blood flow in marijuana users – a discovery that participating scientists attributed to marijuana-influenced narrowing of blood vessels.
“The marijuana users had [pulsatility index] PI values that were somewhat higher than those of people with chronic high blood pressure and diabetes,” study co-author Dr. Ronald Herning said in a Feb. 13, 2005, article on the ScienceDaily website. “However, their values were lower than those of people with dementia. This suggests that marijuana use leads to abnormalities in the small blood vessels in the brain, because similar PI values have been seen in other diseases that affect the small blood vessels.”
Three years after the NIDA study was published, ABC News reported on an Australian analysis that concluded that long-term cannabis exposure “causes brain damage that is equivalent to mild-traumatic brain injury or premature aging.”
“This is a very exciting study because it proves for the first time what we have been really worried out,” Professor Jon Currie, the director of addiction medicine at St Vincent’s Hospital in Melbourne, Australia, said in a June 4, 2008, article on the ABC website. “That brain problems are real and that people who smoke cannabis over a long term do get problems.”
The ABC article said that MRI images of the brains the of 15 chronic marijuana users who were involved in the Melbourne study revealed the following:
• The parts of the brain that regulate memory and emotion, the hippocampus and the amygdala, were significantly smaller in the marijuana users than in the brains of non-users.
• The brain abnormalities that Currie and his colleagues discovered were similar to the damage that can be caused by “a mild traumatic brain injury or premature aging.”
• Study subjects who were in their late 30s had memory function that would be expected of men over the age of 50.
• The level of damage that the researchers noted was proportional to the amount of marijuana that each subject smoked.
When speaking with ABC News, Currie made no secret of his hopes for the impact of his research. “My hope is that this can be used as a very, very clear warning to people,” he said. “Get help, seek medical help, try and stop smoking.”
Environmental factors such as the availability of marijuana, expectations about how the drug would affect them, the influence of friends and social contacts, and other factors that differentiate identical twins’ experiences also were found to have an important effect; however, it also was discovered that the twins’ shared or family environment before age 18 had no detectable influence on their response to marijuana.
Effects of Marijuana on the Brain
Researchers have found that THC changes the way in which sensory information gets into and is processed by the hippocampus. The hippocampus is a component of the brain’s limbic system that is crucial for learning, memory, and the integration of sensory experiences with emotions and motivations. Investigations have shown that neurons in the information processing system of the hippocampus and the activity of the nerve fibers in this region are suppressed by THC. In addition, researchers have discovered that learned behaviors, which depend on the hippocampus, also deteriorate via this mechanism.
Recent research findings also indicate that long-term use of marijuana produces changes in the brain similar to those seen after long-term use of other major drugs of abuse.
Effects on the Lungs
Someone who smokes marijuana regularly may have many of the same respiratory problems as tobacco smokers. These individuals may have daily cough and phlegm, symptoms of chronic bronchitis, and more frequent chest colds. Continuing to smoke marijuana can lead to abnormal functioning of lung tissue injured or destroyed by marijuana smoke.
Regardless of the THC content, the amount of tar inhaled by marijuana smokers and the level of carbon monoxide absorbed are three to five times greater than among tobacco smokers. This may be due to the marijuana users’ inhaling more deeply and holding the smoke in the lungs and because marijuana smoke is unfiltered.
Effects on Heart Rate and Blood Pressure
Recent findings indicate that smoking marijuana while shooting up cocaine has the potential to cause severe increases in heart rate and blood pressure. In one study, experienced marijuana and cocaine users were given marijuana alone, cocaine alone, and then a combination of both. Each drug alone produced cardiovascular effects; when they were combined, the effects were greater and lasted longer. The heart rate of the subjects in the study increased 29 beats per minute with marijuana alone and 32 beats per minute with cocaine alone. When the drugs were given together, the heart rate increased by 49 beats per minute, and the increased rate persisted for a longer time. The drugs were given with the subjects sitting quietly. In normal circumstances, an individual may smoke marijuana and inject cocaine and then do something physically stressful that may significantly increase the risk of overloading the cardiovascular system.
Effects of Heavy Marijuana Use on Learning and Social Behavior
A study of college students has shown that critical skills related to attention, memory, and learning are impaired among people who use marijuana heavily, even after discontinuing its use for at least 24 hours. Researchers compared 65 “heavy users,” who had smoked marijuana a median of 29 of the past 30 days, and 64 “light users,” who had smoked a median of 1 of the past 30 days. After a closely monitored 19- to 24-hour period of abstinence from marijuana and other illicit drugs and alcohol, the undergraduates were given several standard tests measuring aspects of attention, memory, and learning. Compared to the light users, heavy marijuana users made more errors and had more difficulty sustaining attention, shifting attention to meet the demands of changes in the environment, and in registering, processing, and using information. These findings suggest that the greater impairment among heavy users is likely due to an alteration of brain activity produced by marijuana.
Longitudinal research on marijuana use among young people below college age indicates those who used marijuana have lower achievement than the non-users, more acceptance of deviant behavior, more delinquent behavior and aggression, greater rebelliousness, poorer relationships with parents, and more associations with delinquent and drug-using friends.
Research also shows more anger and more regressive behavior (thumb sucking, temper tantrums) in toddlers whose parents use marijuana than among the toddlers of non-using parents.
Effects on Pregnancy
Any drug of abuse can affect a mother’s health during pregnancy, making it a time when expectant mothers should take special care of themselves. Drugs of abuse may interfere with proper nutrition and rest, which can affect good functioning of the immune system. Some studies have found that babies born to mothers who used marijuana during pregnancy were smaller than those born to mothers who did not use the drug. In general, smaller babies are more likely to develop health problems.
A nursing mother who uses marijuana passes some of the THC to the baby in her breast milk. Research indicates that the use of marijuana by a mother during the first month of breast-feeding can impair the infant’s motor development (control of muscle movement).
A drug is addicting if it causes compulsive, often uncontrollable drug craving, seeking, and use, even in the face of negative health and social consequences. Marijuana meets this criterion. More than 120,000 people enter treatment per year for their primary marijuana addiction. In addition, animal studies suggest marijuana causes physical dependence, and some people report withdrawal symptoms.