In 1972, after reviewing the scientific evidence, the National Commission on Marihuana and Drug Abuse concluded that while cannabis was not entirely safe, its dangers had been grossly overstated.
Since then, researchers have conducted thousands of studies of humans, animals, and cell cultures. None reveal any findings dramatically different from those described by the National Commission in 1972. In 1995, based on thirty years of scientific research editors of the British medical journal Lancet concluded that "the smoking of cannabis, even long term, is not harmful to health."
I know people who’ve been prescribed medical marijuana to battle their mental illness. So saying that marijuana can cause some form of mental illness is totally absurd and baseless

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, but it is not as effective as smoked cannabis for many patients. Pure THC may also produce more unpleasant psychoactive side effects than smoked cannabis. Many people use cannabis as a medicine today, despite its illegality. In doing so, they risk arrest and imprisonment.

Most people who smoke cannabis smoke it only occasionally. A small minority of Americans – less than 1 percent – smoke cannabis on a daily basis. An even smaller minority develop a dependence on cannabis. Some people who smoke cannabis heavily and frequently stop without difficulty. Others seek help from drug treatment professionals. Cannabis does not cause physical dependence. If people experience withdrawal symptoms at all, they are remarkably mild.

Cannabis does not cause people to use hard drugs. What the gateway theory presents as a causal explanation is a statistic association between common and uncommon drugs, an association that changes over time as different drugs increase and decrease in prevalence.
Cannabis is the most popular illegal drug in the United States today. Therefore, people who have used less popular drugs such as heroin, cocaine, and LSD, are likely to have also used cannabis. Most cannabis users never use any other illegal drug. Indeed, for the large majority of people, cannabis is a terminus rather than a gateway drug.

Cannabis arrests in the United States doubled between 1991 and 1995. In 1995, more than one-half-million people were arrested for cannabis offences. Eighty-six percent of them were arrested for cannabis possession. Tens of thousands of people are now in prison or cannabis offences.
An even greater number are punished with probation, fines, and civil sanctions, including having their property seized, their driver’s license revoked, and their employment terminated. Despite these civil and criminal sanctions, cannabis continues to be readily available and widely used.

The Netherlands’ drug policy is the most nonpunitive in Europe. For more than twenty years, Dutch citizens over age eighteen have been permitted to buy and use cannabis (cannabis and hashish) in government-regulated coffee shops. This policy has not resulted in dramatically escalating cannabis use, in fact it has reduced occasional and regular usage rates. They are lower than in other European countries, and teenagers find less glamour attached to it because of the absence of a "stigma". The Dutch people overwhelmingly approve of current cannabis policy which seeks to normalize rather than dramatize cannabis use. The Dutch government occasionally revises existing policy, but it remains committed to decriminalization.

None of the medical tests currently used to detect brain damage in humans have found harm from cannabis, even from long term high-dose use. An early study reported brain damage in rhesus monkeys after six months exposure to high concentrations of cannabis smoke. In a recent, more carefully conducted study, researchers found no evidence of brain abnormality in monkeys that were forced to inhale the equivalent of four to five cannabis cigarettes every day for a year.
The claim that cannabis kills brain cells is based on a speculative report dating back a quarter of a century that has never been supported by any scientific study.

For twenty-five years, researchers have searched for a cannabis-induced amotivational syndrome and have failed to find it. People who are intoxicated constantly, regardless of the drug, are unlikely to be productive members of society.
There is nothing about cannabis specifically that causes people to lose their drive and ambition. In laboratory studies, subjects given high doses of cannabis for several days or even several weeks exhibit no decrease in work motivation or productivity.
Among working adults, cannabis users tend to earn higher wages than non-users. College students who use cannabis have the same grades as nonusers. Among high school students, heavy use is associated with school failure, but school failure usually comes first.

Cannabis produces 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 diminishment only lasts for the duration of the intoxication.
There is no convincing evidence that heavy long-term cannabis use permanently impairs memory or other cognitive functions.