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Drug Policy Alliance Marijuana Facts Booklet

additional links on harmful "facts" and factual "harms"

National Institute on Drug Abuse (NIDA) on marijuana

Pot is Bad

What 20 years of research on cannabis use has taught us

Heavy, persistent pot use linked to economic, social problems at midlife

Smoking Weed Makes You a Loser, says study

Long-term cannabis use may blunt the brain's motivation system

Pot Calling Kettle Bad

Maia Szalavita, Don’t Believe the (Marijuana) Hype

Maia Szalavitz, Reefer Inanity: Never Trust the Media on Pot

Kristen Gwynne, Everything Americans Think They Know About Drugs Is Wrong: A Scientist Explodes the Myths

Carl Hart, Why research is biased against pot to focus on its harm and not its benefits

assessing drug harms and drug facts

Drug Policy Alliance - 10 facts about marijuana

Marijuana (Cannabis) Facts

Does marijuana use have long term cognitive effects?

FACT: Marijuana does not cause long-term cognitive impairment in users who start after 21 years old.

The short-term effects of marijuana include immediate, temporary changes in thoughts, perceptions and information processing. The cognitive process most clearly affected by marijuana is short-term memory.

In laboratory studies, subjects under the influence of marijuana have no trouble remembering things they learned previously. However, they temporarily display diminished capacity to learn and recall new information. This diminishment only lasts for the duration of the intoxication.

There is no convincing evidence that heavy long-term marijuana use permanently impairs memory or other cognitive functions. A recent, large-scale, longitudinal study of adult marijuana users corroborates earlier findings that marijuana produces no long-term negative effects on cognition, stating, "The adverse impacts of cannabis use on cognitive functions either appear to be related to pre-existing factors or are reversible . . . even after potentially extended periods of use." However, it is not recommended that adolescents use marijuana unless under the care of a physician, as some research suggests potentially negative cognitive effects for adolescents who use marijuana. It is recommended that individuals delay their marijuana use until adulthood.[9]

What is the relationship between marijuana and cancer?

FACT: Marijuana use is not associated with elevated cancer risk as shown in preclinical studies.

Several longitudinal studies have established that even long-term marijuana smoking is not associated with elevated cancer risk, including tobacco-related cancers or with colorectal, lung, melanoma, prostate, breast or cervix.

A 2009 population-based case-control study found that moderate marijuana smoking over a 20-year period was associated with reduced risk of head and neck cancer. And a five-year-long population-based case-control study found even long-term heavy marijuana smoking was not associated with lung cancer or upper aerodigestive tract cancers.[5]

In fact, some of the chemicals in marijuana, such as THC and especially CBD, have been found to induce tumor cell death and show potential as effective tools in treating cancer. Scientists who have conducted this type of research, such as UCLA’s Donald Tashkin, hypothesize that the anti-oxidant properties of cannabis might override any cancer causing chemicals found in marijuana smoke, therefore protecting the body against the impact of smoking. Newer research indicates that marijuana has anti-cancer properties and could one day unlock new cancer treatments.

Moreover, marijuana smoking is not associated with any other permanent lung harms, such as chronic obstructive pulmonary disorder (COPD), emphysema or reduced lung function – even after years of frequent use. [6]

Are more people becoming dependent on marijuana?

FACT: Rates of marijuana dependence have not increased over the past 10 years.
A landmark, Congressionally-mandated Institute of Medicine study found that fewer than 10 percent of those who try marijuana ever meet the clinical criteria for dependence, while 32 percent of tobacco users and 15 percent of alcohol users do.

As a result of treatment-instead-of-incarceration policies implemented over the past two decades to stem the skyrocketing U.S. prison population, marijuana treatment admissions referred by the criminal justice system rose from 48 percent in 1992 to 52 percent in 2011.

Just 45 percent of people who enter marijuana treatment meet the Diagnostic and Statistical Manual of Mental Disorders criteria for marijuana dependence. More than a third hadn’t used marijuana in the 30 days prior to admission for treatment.

Many people are “discovered” due to the smell of marijuana and forced to choose between jail and treatment. Treatment providers support drug courts because they ensure a steady stream of clients.

Even with this increase in court-mandated marijuana treatment, only 1.1% of marijuana users 12 and older in 2011 went to treatment for it. Twice as many people were arrested for simple marijuana possession that year than entered treatment for marijuana dependence (750,000 vs. 333,578).

Increases in treatment access and emergency room visits related to marijuana use can be the result of the decriminalization of marijuana consumers and the destigmatization of marijuana use. Both of these phenomena would result in consumers feeling more comfortable admitting use and seeking help related to their use.[3]

Is it true that marijuana has medicinal properties?

FACT: Marijuana has been proven helpful for treating the symptoms of a variety of medical conditions. The body's endocannabinoid system may explain why.
For many seriously ill people, medical marijuana is the only medicine that relieves their pain and suffering, or treats symptoms of their medical condition, without debilitating side effects.

Marijuana’s medicinal benefits are incontrovertible, now proven by decades of peer-reviewed, controlled studies published in highly respected medical journals. Marijuana has been shown to alleviate symptoms of wide range of debilitating medical conditions including cancer, HIV/AIDS, multiple sclerosis, Alzheimer’s Disease, post-traumatic stress disorder (PTSD), epilepsy, Crohn’s Disease, and glaucoma, and is often an effective alternative to narcotic painkillers.

Evidence of marijuana’s efficacy in treating severe and intractable pain is particularly impressive. Researchers at the University of California conducted a decade of randomized, double-blind, placebo-controlled clinical trials on the medical utility of inhaled marijuana, concluding that marijuana should be a “first line treatment” for patients with painful neuropathy, who often do not respond to other available treatments.

Marijuana has been shown to be effective in reducing the nausea induced by cancer chemotherapy, stimulating appetite in AIDS patients, and reducing intraocular pressure in people with glaucoma. There is also appreciable evidence that marijuana reduces muscle spasticity in patients with neurological disorders.

Marijuana has also been shown to help with mental health conditions, particularly PTSD. In 2013, both Maine and Oregon added PTSD to the list of conditions that qualifies for medical marijuana. A synthetic capsule is available by prescription, but it is not as effective as smoked marijuana for many patients.

Our bodies contain a regulatory framework called the endocannabinoid system. This system is responsible for maintaining balance or homeostasis in the body. Some scientists theorize that a deficiency in the endocannabinoid system may contribute to certain diseases, such as Crohn’s disease, which may explain why the introduction of phyto-cannabinoids (from the marijuana plant) help alleviate the symptoms of these conditions.

Although an overwhelming majority of Americans support medical marijuana, the federal government continues to impede state medical marijuana laws. Marijuana prohibition has also thwarted research within the United States to uncover the best and most effective uses for marijuana as a medicine, making efforts to reform medical marijuana laws particularly difficult. Learn more about medical marijuana.[7]

Does marijuana affect mental health?

FACT: The majority of adults who use marijuana do not have adverse mental health issues.

Many opponents of medical marijuana make much of the purported link between marijuana use and mental illness. But there is simply no compelling evidence to support the claim that marijuana is a causal risk factor for developing a psychiatric disorder in otherwise healthy individuals. Most tellingly, population-level rates of schizophrenia or other psychiatric illnesses have remained flat even when marijuana use rates have increased.

Emerging evidence indicates that patients who have tried marijuana may show significant improvements in symptoms and clinical outcomes (such as lower mortality rates and better cognitive functioning ) compared with those who have not. In fact, some of the unique chemicals in marijuana, such as cannabidiol (CBD), seem to have anti-psychotic properties.

Researchers are investigating marijuana as a possible source of future schizophrenia treatments; until it is legalized, however, this research is significantly impeded.

Rates of mental illness have remained stable in light of changes in marijuana consumption levels. For example, when marijuana use rates have increased, there have been no increases in schizophrenia diagnoses.

We do see these types of correlations, however for other behaviors that are connected. For example, rates of diabetes in the U.S. have increased as obesity rates have increased. This is not to say, however, that there is no relationship between psychoactive substances and mental functioning. Some effects of marijuana use can include feelings of panic, anxiety and paranoia. Such experiences can be frightening, but the effects are temporary.

Some psychoactive substances have been shown to improve mental health functioning and some do not. Recent research at the University Medical Center Utrecht in the Netherlands concluded that the endocannabinoid system is responsible for making chemicals that combat mental health conditions such as depression. Stimulating the endocannbinoid system via the use of cannabinoids found in the cannabis plant might hold promise as a treatment for depressions and other mental health conditions. Part of the reason that is it so difficult to detangle psychoactive substance use from mental health is age of onset.

For most people, symptoms of mental disturbance occur in the late teens and early 20’s. While it is impossible to predict who will develop a mental disturbance, there seem to be some ties to genetics and to behavioral cues in early childhood. Those who have risk factors, such as a family history of mental health issues, should be cautious in their exposure to all substances that have any intoxicating effects.

Unfortunately, in adolescence, teens are more likely to experiment with intoxicants and less likely to be open with their parents about their drug use and/or any symptoms of mental disturbance they may be experiencing. As a result, drug and alcohol use has usually already started by the time symptoms of mental illness become noticeable.

This is why we see so many studies that confirm that most people diagnosed with severe mental illness have had a history of alcohol and drug use. The alcohol and drug use was not the cause of the mental illness, but rather a behavior that coincides with the undetected development of mental health symptoms. In fact, research suggests that those with mental illness might be self-medicating with marijuana.

One study demonstrated that psychotic symptoms predict later use of marijuana, suggesting that people might turn to the plant for help rather than become ill after use. However, it should be noted that studies of marijuana as a "treatment" for certain mental health disorders are in preliminary phases, and there is no mental health condition for which marijuana is a standard of care treatment.

These findings have been replicated by myriad other studies, including a new study conducted by Harvard University researchers, which found that marijuana “is unlikely to be the cause of illness,” even in people who may be genetically predisposed to schizophrenia or other psychotic disorders. The researchers concluded, "In summary, we conclude that cannabis does not cause psychosis by itself. In genetically vulnerable individuals, while cannabis may modify the illness onset, severity and outcome, there is no evidence from this study that it can cause the psychosis."

Encouraging an open dialogue with adolescents about their drug use and paying attention to their behavior during the teen years are better prevention tools toward the future development of mental illness than to simply blame marijuana.[5]


Drug Policy Alliance 10 Facts About Marijuana pdf
July 25, 2014
These are ten top facts about marijuana policy and effects, with detailed supporting information and citations.