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How Harmful is Marijuana?
Pages 38-70

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From page 38...
... Although free of nicotine, marijuana smoke certainly pollutes the lungs. And since tobacco smoking has been linked to respiratory injury, cancer, emphysema, heart disease, complications of pregnancy, low birth weight, and other ills, it makes sense to worry whether smoking marijuana might prove equally harmful.
From page 39...
... On the one hand, marijuana joints have been shown to deliver at least four times as much tar to the lungs as tobacco cigarettes of equivalent weight. This difference is due to the lack of filters on joints and because marijuana smokers typically inhale a larger volume of smoke and take it more deeply into the lungs than tobacco smokers do.
From page 40...
... In this study of habitual marijuana smokers, participants who smoked both marijuana and tobacco reported no more symptoms of chronic bronchitis overall than those who smoked tobacco alone, an indication that smoking marijuana does not increase the harms caused by smoking tobacco. Another study did show evidence of such an interaction, but it was conducted on people who smoked considerably less marijuana and tobacco than those who participated in the previously described study.
From page 41...
... Preliminary research also suggests that marijuana smokers' lung cells contain higher levels of an enzyme that converts PAHs into a cancer-causing form. Thus, it is not surprising that several studies implicate marijuana smoking
From page 42...
... More than 30 years have elapsed since the start of widespread marijuana use among young people in the United States, who now constitute a sufficiently large population to support meaningful epidemiological studies. On the other hand, such surveys are difficult to conduct, since far fewer people have smoked marijuana exclusively than have smoked tobacco alone and also because marijuana smokers are likely to underreport their use of the illegal drug.
From page 43...
... Similar alterations have been detected in the actual lung cells of marijuana smokers and at even higher levels among those who also smoked tobacco. An especially convincing study evaluated changes in blood cells taken from pregnant women who were exclusive smokers of marijuana and also from their babies after they were born.6 In a class of white blood cells called lymphocytes, the researchers found significantly more DNA aberrations of a type linked to cancer development as compared with lymphocytes from nonsmoking women and their newborns.
From page 44...
... Both experiments suggest that the timing of THC exposure relative to infection determines whether THC suppresses the immune response.8 Even if cannabinoids themselves cause little or no harm to the immune system, there is good reason to believe that smoking marijuana does. Marijuana smoke been linked to increased mortality in people with AIDS and it also appears to injure an important class of immune cells in the lungs.
From page 45...
... Compared with nonsmokers, habitual marijuana smokers in a large study were found to have twice as many alveolar macrophages, a sign that their lungs were fighting infection or invasion. People who smoked both marijuana and tobacco had four times as many of the cells as nonsmokers.9 Marijuana smoking was also found to reduce the ability of alveolar macrophages to destroy disease-causing fungus and bacteria as well as tumor cells.
From page 46...
... Marijuana smoke appears to pose an even greater threat to pregnant women and couples who are trying to conceive, since it is probably at least as harmful to fetal development as tobacco smoke. Several epidemiological studies have attempted to trace the effects of marijuana use on pregnancy and fetal development, but their results have been inconsistent.
From page 47...
... In the meantime it appears that, for people with chronic medical disorders or those with compromised respiratory or immune systems, smoking marijuana is likely to do more harm than good. Likewise, for people at risk of cardiovascular disease, pregnant women, and couples trying to conceive, the potential risks of either THC or smoked marijuana appear to exceed the potential medical benefits.
From page 48...
... If someone who is physically dependent on a drug stops taking it, he or she is likely to experience withdrawal symptoms. Most drugs that are abused produce tolerance, physical dependence, and withdrawal but so do caffeine and nicotine as well as many nonaddictive drugs for pain, anxiety, and high blood pressure.
From page 50...
... The marijuana-smoking group reported feeling "mellow" after smoking throughout the four days, while the THC-taking group never reported feeling "mellow." The IOM team also heard from several people who had tried both smoked marijuana and oral THC to treat their medical symptoms and whose comparisons of the two drugs resembled those of the study participants. In addition to human studies, scientists have conducted research on animals to study how tolerance to cannabinoids arises.
From page 51...
... Still, some of the same biochemical responses to chronic cannabinoid exposure that have been observed in experimental animals probably occur in humans as well, though perhaps in subtler forms. Withdrawal from either marijuana or THC has been shown to cause several distinct symptoms, as reported by participants in clinical studies and adolescents undergoing treatment for substance abuse.
From page 52...
... A similar situation probably occurs in human marijuana users who go "cold turkey," easing the process of withdrawal. However, by administering a chemical block that immediately interferes with THC's effects, researchers can create a sort of instantaneous withdrawal in experimental animals that have been chronically exposed to THC.
From page 53...
... As people progress from tolerance to physical dependence to drug abuse, their craving intensifies despite mounting problems caused by their behavior. This intense desire for a drug is the toughest part of addiction to overcome.
From page 54...
... It has not specifically addressed marijuana, so it remains unknown whether marijuana induces similar changes in brain function. MAR[ UANA USE AND DEPENDENCE Another way to look at the risk of marijuana addiction is to examine general patterns of use and dependence.
From page 55...
... But people who turn to marijuana to relieve medical symptoms most of whom are older than 35 face an entirely different set of circumstances than do youthful recreational users. There are no existing scientific studies of the relationship between medical marijuana use and abuse.
From page 56...
... People with psychiatric disorders constitute another group at high risk for drug abuse. An estimated 76 percent of men and 65 percent of women classified as being drug dependent suffer from at least one additional psychiatric disorder; most frequently, that disorder is alcohol abuse.
From page 57...
... 1994. Comparative epidemiology of dependence on tobacco, alcohol, controlled substances, and inhalants: Basic findings from the National Comorbidity Survey.
From page 58...
... Indeed, some of the psychoactive effects of marijuana such as anxiety reduction, sedation, and euphoria can be counted among the drug's potential benefits for certain patients. This paradox, plus the fact that the vast majority of research on the psychological effects of marijuana and cannabinoids concerns intoxication and recreational use, makes it difficult to anticipate the psychological impact of medical marijuana use.
From page 59...
... These symptoms usually disappear within hours and respond well to reassurance and a supportive environment. Seventeen percent of regular marijuana smokers report that they have experienced at least one of these symptoms at some time typically early in their use of the drug.
From page 60...
... When heavy marijuana use accompanies this behavior, the drug is often cited as the cause, despite the fact that no convincing data demonstrate that marijuana actually provokes these symptoms. It is not enough to observe that chronic marijuana users lack drive or ambition.
From page 61...
... Some researchers have argued that the diversity of these symptoms belies the existence of a specific "marijuana psychosis." Others have concluded that heavy marijuana use and perhaps even acute use in especially sensitive people can produce a psychosis characterized by a suite of symptoms such as confusion, amnesia, delusions, hallucinations, anxiety, and agitation. Regardless of which of these interpretations is correct, both camps agree that marijuana use alone without the influence of additional risk factors is unlikely to provoke a psychosis that persists longer than intoxication.30 Drug abuse is common among people with mental illness.
From page 62...
... MEDICAL MAR dUANA: A DANGER TO SOCIETY? Almost everyone who spoke or wrote to the IOM study team about medical marijuana's potential harms felt that acknowledgment of marijuana's possible medical value would undermine its reputation as a dangerous drug, particularly among young people.
From page 63...
... People who are most likely to use illicit drugs other than marijuana tend to share several traits, including use of alcohol or nicotine at an early age, heavy marijuana use, and psychiatric disorders. Yet while it appears that people who try alcohol and nicotine earliest are more likely than others to experiment with illegal drugs, they are no more likely to become heavy drug users.
From page 64...
... At present, data on drug use neither support nor refute the assertion that legalizing marijuana for medical purposes would prompt increased drug abuse among medical marijuana users. A related but distinct concern is whether the use of marijuana for medical purposes would encourage drug use throughout society in general.
From page 65...
... However, reasonable inferences can be drawn about the outcome of such a change based on three examples: patterns of abuse for opiate drugs, including painkillers such as morphine and codeine; patterns of drug abuse in the Netherlands and also in some parts of the United States, where marijuana was decriminalized in the 1970s; and the short-term consequences of the campaign to legalize medical marijuana in California in 1996. Opiates can be considered a "stand-in" for marijuana-based medicines since both classes of drugs have the potential to be abused to great harm as well as to be used for medical benefit.
From page 66...
... According to the most recent National Household Survey on Drug Abuse, significantly fewer children between the ages of 12 and 17 reported that they perceived marijuana as a "great risk of harm" in 1997 than in 1996.36 At first glance this might seem to validate the fear that the medical marijuana debate of 1996 prior to passage of the California medical marijuana referendum in November 1997 had caused more teenagers to believe that marijuana use is safe. But a closer analysis of the data show that, de
From page 67...
... Marijuana smoke, like tobacco smoke, is associated with increased risk of cancer, lung damage, and poor pregnancy outcomes. Smoked marijuana is thus unlikely to prove to be a safe medication for any chronic medical condition.
From page 68...
... 1993. "Health care use by frequent marijuana smokers who do not smoke tobacco." The Western Journal of Medicine 158:596-601.
From page 69...
... 1987. "Differential examination of bronchoalveolar ravage cells in tobacco cigarette and marijuana smokers." American Review of Respiratory Disease 135:1271-1275.
From page 70...
... 1998. National Household Survey on Drug Abuse: Population Estimates 1997.


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