March 24, 2007

Cannabis Use / Schizophrenia Correlation Being Studied

Researchers are studying historic trends in cannabis (marijuana) use in the United Kingdom, matching them to new cases of schizophrenia. If, as a significant amount of evidence shows, cannabis use contributes to the risk, or triggers schizophrenia in vulnerable individuals, then very soon, it will be accounting for 10% of all new cases of schizophrenia in Wales and Britain, with increases in schizophrenia starting earlier among young men in particular.

Researchers, in their published article in Addiction Journal, say that exposure to cannabis quadrupled in the 30 years prior to 2002. Its use in children under 18 grew 18-fold.

Some researchers suggest that if cannabis use truly triggers schizophrenia, then a rise in the number of new cases of schizophrenia should be seen. Model projections of onset of disease have been made based on heavy cannabis use, as well as on light use. According to model projections (based on historical data), by 2010 about 10% of new cases of schizophrenia could be due to heavy cannabis use. If even light use of cannabis triggers schizophrenia, then about one fourth of new cases (25%) could be due to cannabis use by 2010.

Matthew Hickman, lead author of the study, says:

"The challenge now is to improve our data on schizophrenia occurrence to see whether the projected increase occurs. This will tell us more about how important cannabis is as a cause of schizophrenia."

Thanks goes to Elda for bringing this article to our attention.

Read the full article:

Substantial increases in both prevalence and incidence of the disease are forecast by the end of the decade, with increases in schizophrenia starting earlier among young men in particular.

The research study matches historic trends in cannabis use and exposure from a national population survey against estimates of new occurrences of schizophrenia in three English cities (Nottingham, Bristol and the London Borough of Southwark).

The researchers assess what might happen to schizophrenia cases if we assume a causal link between cannabis use and onset of psychotic symptoms, an association widely recognised by some psychiatrists and researchers and considered recently by the Advisory Council on the Misuse of Drugs.

Exposure to cannabis grew fourfold over the thirty years to 2002, and its use among under-18s by 18-fold, say the researchers. If cannabis use causes schizophrenia, these increases in its use would lead to increases in overall schizophrenia incidence and prevalence of 29 per cent and 12 per cent respectively, between 1990 and 2010. (Incidence is defined as the frequency of new occurrences; and prevalence is the percentage of the population affected by the disease.)

Model projections suggest that if the association is confined to heavy cannabis users only, then approximately 10 per cent of schizophrenia cases may be due to cannabis by 2010. However, assuming an association between onset of the disease and both light and heavy users, then approximately one-quarter of new cases could be due to cannabis.

John Macleod, co-author and academic GP, said: “We need to remember that our study does not address the question whether cannabis causes schizophrenia: this remains unclear.”

Matthew Hickman, lead author of the study, added: “The challenge now is to improve our data on schizophrenia occurrence to see whether the projected increase occurs. This will tell us more about how important cannabis is as a cause of schizophrenia.”

Reference: Cannabis and schizophrenia: model projections of the impact of the rise in cannabis use on historical and future trends in schizophrenia in England and Wales (2007). Addiction 102 (4), 597-606.

Related Reading:
UK Charity Pushes for National Cannabis / Marijuana Education on Link to Schizophrenia
Public Education Program on Marijuana / Schizophrenia Link Working (in Australia)
Cannabis Abuse May Lead to Earlier Schizophrenia Onset, Worse Outcome
Cannabis and Psychosis (schizophrenia) and the COMT gene
Marijuana and Schizophrenia - Public Policy Implications


Without a doubt in my mind I do believe that heavy usage of cannabis definitely does and almost in every case I've seen leads to schizophrenic psychosis. Having been a heavy cannabis user, i had always thought it was just me who had developed this psychosis, but it is a pattern that is obvious in so many other people I know who use cannabis on a regular basis. The link between cannabis and schizophrenia is VERY STRONG

Posted by: Cheong at April 2, 2007 05:39 AM

I developed schizophrenia when I was 31. I have also, occasionally, used cannabis. When I do, it has no effect on my schizophrenia. I am not convinced that the correlation between use of drugs and schizophrenia proves that taking drugs causes schizophrenia. There are other issues that could explain this correlation. I find that my voice often talks to me about ethical issues. For a long time it spoke to me about whether it was ethical to take drugs or not. In other words, the fact that drugs are illegal is a stress factor for anyone who takes drugs. For some people, taking drugs poses more serious stress. It may mean that they are associating with criminals. To me it is not surprising that people taking drugs are more likely to develop schizophrenia, so long as drugs are illegal. I consider that it is possible that if drugs were not prohibited, I would not have developed schizophrenia.

Posted by: Colin at April 4, 2007 01:32 PM

Hi Colin,
maybe not the place on the site to discuss this (should be in forums I guess), but from my personal expirience - strong corellation exists. I won't go into detials, but in my example, it was like a causal reaction, first bad state of mind during enjoying marijuana, then it continued in days after, then slowly it turned into schizophrenia. I am strongly against it - but it does not affect all people in the same way. It is only that some people react badly on it, not everybody.

Posted by: Maria at April 8, 2007 09:08 AM

The glutamate hypothesis, there is the link between the NMDA receptor hypofunction and schizophrenia. The goal of my comment is to show that cannabis use can be a proof about this "NMDA link". See my website , chapter; Hyperfunction (Alzheimer’s disease and Parkinson disease) and hypofunction (schizophrenia) of glutamatergic neurons. See also my opinion- articles in Medical News Today and I think that marijuana is a serious problem, because according to the science studies it seems that cannabis use can precipitate schizophrenia in vulnerable individuals (alkoholism, undernutrition…), especially. However, there are other studies about the opposite marijuana effect, so scientists say; „One possibility is that there are good guys and bad guys within cannabis… Maybe the cannabidiol ameliorates some of the effects of the THC and maybe it actually might be good for you if you are psychotic“. I would like to show that there can be a "nutritional theory" (different „body calcium status“ in good and bad guys…) about the cause of schizophrenia based on "calcium deficiency"...

Posted by: Josef Hlasny at September 5, 2007 04:36 AM

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