“Since 2002, a series of ten such studies have reported that individuals who used cannabis at the baseline evaluation had a greater risk of subsequently developing psychotic symptoms and indeed full-blown schizophrenia than non-users. “

  • …”Since 2002, a series of ten such studies have reported that individuals who used cannabis at the baseline evaluation had a greater risk of subsequently developing psychotic symptoms and indeed full-blown schizophrenia than non-users. Other studies of cannabis users who had sought medical care showed that they had a marked increased risk of subsequent schizophrenia. Such unanimity is rare in psychiatric epidemiology.”
  • “Cannabis is now generally accepted as a cause of schizophrenia (though less so in North America, where this topic has received little attention). Argument does continue over just how significant cannabis-associated psychosis is. In different countries, the proportion of schizophrenia attributed to cannabis use ranges from 8 to 24 percent, depending, in part, on the prevalence of cannabis use.”
  • “Nevertheless, the vast majority of users won’t become psychotic.…It appears that some people are especially vulnerable. Not surprisingly, people with a paranoid or “psychosis-prone” personality are at greatest risk, alongside people with a family history of psychosis. Research also suggests that inheriting certain variants of genes that influence the dopamine system, which is implicated in psychosis, may make some users especially susceptible…”
  • “the increasing availability of high-potency types of cannabis explains why psychiatrists should be more concerned about cannabis now than they were in the 1960s and 1970s.”
  • “In picking their way through the conflicting views, politicians and regulators need to recognize that “medicinal marijuana” has become largely a cover for introducing recreational use by the marijuana industry”

Appraising the Risks of Reefer Madness
By: Sir Robin Murray, M.D.

Editor’s Note: Studies that have tied cannabis use to schizophrenia in the developing brain are just the tip of the iceberg when it comes to marijuana.
Cerebrum – January 2015 – article – feature

Beginning in the mid-1980s, European psychiatrists like me started seeing an increasing number of previously well-functioning teenagers who had developed hallucinations and delusions: the characteristic picture of schizophrenia…My view began to shift when a colleague, Peter Allebeck from the Karolinska Institute in Stockholm, launched his own investigation. He had been struck similarly by seeing well-adjusted young people develop schizophrenia for no apparent reason. The wonderful Swedish national records system enabled him to trace the outcome of 45,750 young men who had been asked about their drug use when they were conscripted into the Swedish army. From analysis of these data, Allebeck and his colleagues1 reported in 1987 that conscripts who had used cannabis more than fifty times were six times more likely to develop schizophrenia over the next fifteen years than those who had never used it.

Because only one study existed, most psychiatrists reassured themselves that the cannabis users probably were destined for schizophrenia before they started smoking. As a result, Allebeck’s findings were mostly ignored. Even the prestigious medical journal The Lancet, which had published Allebeck’s paper, carried an editorial in 1995 that restated the prevailing medical view that “the smoking of cannabis, even long term, is not harmful to health.”2

…some suggested, psychotic patients used cannabis to “self-medicate” or otherwise help them to cope with their illness, then one might expect the persistent cannabis users to have a better outcome. But we found the opposite; four years later, the patients who continued to use cannabis were much more likely to still have delusions and hallucinations. Many studies have replicated the findings.

…Since 2002, a series of ten such studies have reported that individuals who used cannabis at the baseline evaluation had a greater risk of subsequently developing psychotic symptoms and indeed full-blown schizophrenia than non-users. Other studies of cannabis users who had sought medical care showed that they had a marked increased risk of subsequent schizophrenia. Such unanimity is rare in psychiatric epidemiology.

A Hostile Reaction
Much of the scientific establishment greeted these findings with hostility, as did people advocating a more liberal attitude regarding cannabis use. My colleagues and I were accused of being closet prohibitionists; some suggested we were experiencing our own kind of “reefer madness.” Critics suggested that people using cannabis were doing so because they were odd and destined to develop schizophrenia anyway.

…. Cannabis is now generally accepted as a cause of schizophrenia (though less so in North America, where this topic has received little attention). Argument does continue over just how significant cannabis-associated psychosis is. In different countries, the proportion of schizophrenia attributed to cannabis use ranges from 8 to 24 percent, depending, in part, on the prevalence of cannabis use.

Excess Becomes a Major Concern
Most people enjoy cannabis in moderation and suffer few or no adverse effects. People take comfort in knowing that some of the most celebrated role models on the planet—Paul McCartney, Oprah Winfrey, and Barack Obama, for example—have admitted to smoking cannabis with no ill effect. But the scientific consensus is that, although there is no convincing evidence of a link to anxiety26 or depression, cannabis can lead to psychosis when consumed in large amounts. The bottom line: daily users who smoke large amounts are increasing their risk of schizophrenia.

Nevertheless, the vast majority of users won’t become psychotic. Indeed, when young people who have developed schizophrenia after years of smoking cannabis are asked whether they think their habit may have contributed, they often say, “No, my friends smoke as much as I do, and they’re fine.” It appears that some people are especially vulnerable.

Not surprisingly, people with a paranoid or “psychosis-prone” personality are at greatest risk, alongside people with a family history of psychosis. Research also suggests that inheriting certain variants of genes that influence the dopamine system, which is implicated in psychosis, may make some users especially susceptible; examples of such genes include AKT1, DRD2, and possibly COMT.

Another important question is: Are some types of cannabis more risky than others?

The Changing Nature of Cannabis
The cannabis plant…produces compounds known as cannabinoids in glandular trichomes, mostly around the flowering tops of the plant. Recreational cannabis is derived from trichomes…Cannabis acts on the CB1 cannabinoid receptor, part of the endocannabinoid system, which helps to maintain neurochemical stability in the brain. The cannabis plant produces more than 70 cannabinoids, but the most important are tetrahydrocannabinol (THC) and cannabidiol (CBD). THC is responsible for the “high” that users enjoy. It activates the cannabinoid CB1 receptor, which is one of the most widespread receptors in the brain.

– The proportion of THC in traditional marijuana and resin in the 1960s was approximately 1 to 3 percent.
– The potency of cannabis began to rise in the 1980s
– By the early years of the twenty-first century in England and Holland, respectively, the potency…, as measured by the proportion of THC, had risen to between 16 and 20 percent, and it had taken over much of the traditional market from resin.

…surprisingly little formal scientific research has explored THC’s effects in humans.

…cannabidiol (CBD), the other main ingredient of traditional cannabis)…Thus, CBD appeared to counter the psychotogenic effects of THC. A German clinical trial…CBD had antipsychotic actions equivalent to a standard antipsychotic, amisulpride, in patients with schizophrenia.

High-potency types of cannabis…differ from traditional forms not only in the amount of THC they contain but also in the proportion of CBD. Interestingly, plants bred to produce a high concentration of THC cannot also produce a lot of CBD, so the high THC types of cannabis contain little or no CBD.

Might high potency types of cannabis be more likely, therefore, to induce psychosis than traditional forms?…Those who had been using high-potency cannabis (skunk) had a much higher risk of psychosis than users of resin. People using skunk-like cannabis on a daily basis were five times more likely than non-users to suffer from a psychotic disorder while users of traditional resin did not differ from non-users. Another study which tested hair for cannabinoids showed that those users with both detectable THC and CBD in their hair had fewer psychotic symptoms than those with only THC.40

Thus the increasing availability of high-potency types of cannabis explains why psychiatrists should be more concerned about cannabis now than they were in the 1960s and 1970s….

Dependence and Cognitive Impairment Remain Controversial
While psychological dependence and tolerence occur, the issue of physical dependence remains hotly debated.

…Under ordinary circumstances, withdrawal symptoms are absent because cannabis remains in the body for several weeks—so withdrawal is very gradual and not obvious, though anxiety, insomnia, appetite disturbance, and depression can develop…cannabis dependence is an increasingly common cause of those seeking help in Australia, Europe, and North America.45-47

Another controversial issue is cognitive impairment. THC disrupts the hippocampus, the area of the brain crucial to memory. When Paul Morrison induced psychotic symptoms by giving intravenous THC to volunteers, transient cognitive impairment also emerged . Such impairment likely is why drivers under the influence of cannabis are at double the risk of traffic accidents.

Heavy users show cognitive impairment, but disagreement continues over what happens when they stop……people who started to use cannabis at age eighteen or later showed only a small, non-significant increase in the risk of schizophrenia-like psychosis by age twenty-six. But among those starting at age fifteen or earlier, the risk increased fourfold. Other studies have reported similar disparities.…..

Implications
A curious divide has opened up between North America and Europe. In the U.S., cannabis use in young people has increased since the mid-1990s as the number regarding use of cannabis as risky has fallen. In contrast, use has fallen in many European countries, partly because of greater knowledge of the risks to mental health.

In picking their way through the conflicting views, politicians and regulators need to recognize that “medicinal marijuana” has become largely a cover for introducing recreational use by the marijuana industry…

Europeans are watching the evolution of the cannabis debate in the U.S. with great interest…

See more at: http://www.dana.org/Cerebrum/2015/Appraising_the_Risks_of_Reefer_Madness/#sthash.sg3YPfaL.dpuf

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