10 February 2013
Cannabis is a plant containing a psychoactive chemical, tetrahydrocannabinol (THC), in its leaves, buds and flowers. Cannabis is the most commonly used illicit drug in the US, with 42% of American adults reporting that they have used it.
Despite the fact that cannabis' effects are less harmful than those of most other drugs, including alcohol and tobacco, it is the most common drug that people are arrested for possessing in the US. US Cannabis policy is unique among American criminal laws in being enforced so widely and harshly, yet deemed unnecessary by such a substantial portion of the population.
Cannabis does not cause people to use hard drugs. Cannabis, being the most popular illegal drug in the US today, leads to people who have used less popular drugs such as heroin, cocaine, and LSD, having likely also used cannabis Most cannabis users never use any other illegal drug and the vast majority of those who do try another drug never become addicted or go on to have associated problems. Indeed, for the large majority of people, cannabis is a terminus rather than a so-called gateway drug.
According to a US Federal Institute of Medicine study in 1999, fewer than 10% of those who try cannabis ever meet the clinical criteria for dependence, while 32% of tobacco users and 15% of alcohol users do. According to US federal data, cannabis treatment admissions referred by the criminal justice system rose from 48% in 1992 to 58% in 2006. Just 45% of cannabis admissions met the Diagnostic and Statistical Manual of Mental Disorders criteria for cannabis dependence. More than a third hadn’t used cannabis in the 30 days prior to admission for treatment.
Although cannabis potency may have increased somewhat in recent decades, claims about enormous increases in potency are vastly overstated and not supported by evidence. Nonetheless, potency is not related to risks of dependence or health impacts. According to the US federal government's own data, the average THC in domestically grown cannabis – which comprises the bulk of the US market – is less than 5%, a figure that has remained unchanged for nearly a decade. In the 1980s, by comparison, the THC content averaged around 3%. Regardless of potency, THC is virtually non-toxic to healthy cells or organs, and is incapable of causing a fatal overdose. Currently in the US, doctors may legally prescribe Marinol, an FDA-approved pill that contains 100% THC. The Food and Drug Administration found THC to be safe and effective for the treatment of nausea, vomiting, and wasting diseases. When consumers encounter unusually strong varieties of cannabis, they adjust their use accordingly and smoke less.
Some effects of cannabis ingestion may include feelings of panic, anxiety, and paranoia. Such experiences can be frightening, but the effects are temporary.
That said, none of this is to suggest that there may not be some correlation (but not causation) between cannabis use and certain psychiatric ailments. Cannabis use can correlate with mental illness for many reasons. People often turn to the alleviating effects of cannabis to treat symptoms of distress. One study demonstrated that psychotic symptoms predict later use of cannabis, suggesting that people might turn to the plant for help rather than become ill after use.
Several longitudinal studies have established that even long-term use of cannabis (via smoking) in humans is not associated with elevated cancer risk, including tobacco-related cancers or with cancer of the following sites: colorectal, lung, melanoma, prostate, breast, cervix. A more recent (2009) population-based case-control study found that moderate cannabis smoking over a 20 year period was associated with reduced risk of head and neck cancer (See Liang et al). And a 5-year-long population-based case control study found even long-term heavy cannabis smoking was not associated with lung cancer or UAT (upper aerodigestive tract) cancers.
Cannabis 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 cannabis reduces muscle spasticity in patients with neurological disorders. A synthetic capsule is available by prescription in the US, but it is not as effective as smoked cannabis for many patients. Learn more about medical cannabis. 
The Netherlands' drug policy is one of the most nonpunitive in Europe. For more than twenty years, Dutch citizens over age eighteen have been permitted to buy and use cannabis (marijuana and hashish) in government-regulated coffee shops. This policy has not resulted in dramatically escalating cannabis use. For most age groups, rates of cannabis use in the Netherlands are similar to those in the United States. However, for young adolescents, rates of cannabis use are lower in the Netherlands than in the United States. The Dutch government occasionally revises existing cannabis policy, but it remains committed to decriminalization.
The short-term effects of cannabis include immediate, temporary changes in thoughts, perceptions, and information processing. The cognitive process most clearly affected by cannabis is short-term memory. In laboratory studies, subjects under the influence of cannabis have no trouble remembering things they learned previously. However, they display diminished capacity to learn and recall new information. This diminishing in capacity only lasted for the duration of the intoxication. There is no convincing evidence that heavy long-term cannabis use permanently impairs memory or other cognitive functions.
At some doses, cannabis affects perception and psychomotor performance – changes which could impair driving ability. However, in driving studies, cannabis produces little or no car-handling impairment – consistently less than produced by low to moderate doses of alcohol and many legal medications. In contrast to alcohol, which tends to increase risky driving practices, cannabis tends to make subjects more cautious. Surveys of fatally injured drivers show that when THC is detected in the blood, alcohol is almost always detected as well. For some individuals, cannabis may play a role in bad driving. The overall rate of highway accidents appears not to be significantly affected by cannabis' widespread use in society.
US police prosecuted 858,408 persons for cannabis violations in 2009, according to the Federal Bureau of Investigation’s annual Uniform Crime Report. Cannabis arrests comprise more than one-half (approximately 52%) of all drug arrests reported in the US. A decade ago, cannabis arrests comprised just 44% of all drug arrests. Approximately 46% of all drug prosecutions nationwide are for cannabis possession. Of those charged with cannabis violations, approximately 88% (758,593 Americans) were charged with possession only. The remaining 99,815 individuals were charged with “sale/manufacture,” a category that includes virtually all cultivation offenses.
Adapted from an article by the Drug Policy Alliance