11717A study from the University of Pittsburgh which denies the mental health hazards of marijuana is surprising, since there are many other scientific studies pointing to a causal or trigger relationship between marijuana use and psychosis potentially developing into schizophrenia. The Pittsburgh study is limited by its small size; reliance on self-reporting and lack of diversity. In fact, the sample size of 408 was 55% African American and included virtually no Hispanics or Asians. It began in 1987, when the THC in marijuana was lower. Read Dr. Christine Miller’s article on Marijuana Myths.
Research in the UK[i] reveals than one in four serious mental disorders are a result of “skunk” (i.e. high THC pot) including schizophrenia and bipolar disorder. Another study of youth in Australia and New Zealand showed teens who used cannabis 7x more likely to attempt suicide, a serious concern which should alarm anyone.
Cannabis Cup competitions sponsored by High Times magazine have pot growers competing to see how high they can increase THC content in their product. These events over the last three decades have made “skunk” pot the norm here in the U.S. In the last 30 years the psychoactive ingredient THC in marijuana has increased six-fold according to Smart Approaches to Marijuana.[ii]
Old-fashioned marijuana or hash which contained the component CBD, also called cannabidiol, did not have as many adverse effects. Or, at least the adverse effects didn’t come on so quickly as they can with today’s highly potent pot. CBD has been largely bred out of the marijuana grown in California, while the THC content has climbed from about 4-6% in 1996 to today’s “skunk” which averages 16%. Concentrated hash oil can be as high as 96% THC, and is being packaged and sold in quantities that are potentially lethal. California’s Emerald Triangle provides 60% of the US marijuana market, according to some of the state legislators. 
An oft heard claim is that marijuana is safer than alcohol. A Finnish study of 18,478 psychosis patients found the highest risk of schizophrenia (46%) was among those with cannabis-induced psychosis, as compared to amphetamines (30%) and alcohol (5%). [iii]
An Australian study [iv] revealed that 4 out of 5 people with schizophrenia were heavy cannabis users during adolescence. Dr. Campbell, who conducted the studies, said that “….. many people used cannabis for years before succumbing to schizophrenia. The psych wards are full of these people.”
The British Medical Journal article of 23 November 2002 — the best long-term study of marijuana and schizophrenia — proves that the mental illness susceptibility is not only a problem with the high-THC marijuana and “dabs” used today. It involved more than 50,000 Swedish men ages 18-20 and followed them 26 years. It factored in variables such as socio-economic status, low IQ, other drug usage, cigarette smoking and existing personality traits. “Cannabis use is associated with an increased risk of developing schizophrenia consistent with causal relationship. This association is not explained by use of other psychoactive drugs or personality traits.” The study involved the low-THC cannabis of the ’70s, ’80s and ’90s. With the old-fashioned marijuana of that time, it was determined that the risk for developing schizophrenia increased once a person used pot 50 times. For those who never used pot at all, there was zero chance of developing schizophrenia.
[i] http://dailymail.co.uk/news/article – 2953915/Scientists-cannabis-TRIPLES-psychosis-ris-Groundbreaking-research-blames-skunk-1-4 new mental disorders. 14 February 2015.
[ii] https://learnaboutsam.org/the-issues/big-marijuana-claims-vs-the-science/#_edn16
[iii] http://www.psychiatrist.com/JCP/article/Pages/2013/v74n01/v74n0115.aspx
[iv] Dr. Andrew Campbell of the NW Mental Health Review Tribunal, Daily Mail (UK), The Australian. Nov 22, 2005
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