I've been very wary of the pro-pot crowd over the past several years - and this piece of research explains why. Yet there are a lot of people promoting weed as a creativity booster (although all of the "evidence" is anecdotal, not based on research) under the assumption that it promotes divergent thinking and/or seeing patterns that one might not otherwise perceive.

But the research suggests the cannabis use has a much darker side than most (any?) users might want to accept. Here are a few links to research on the connection between weed and psychosis.

• Arseneault, L., Cannon, M., Witton, J. & Murray, R.M. (2004). Causal association between cannabis and psychosis: examination of the evidence. The British Journal of Psychiatry, 184: 110-117. doi: 10.1192/bjp.184.2.110
• Fusar-Poli, P., Crippa, J.A., Bhattacharyya, S., Borgwardt, S.J., Allen, P. et al. (2009). Distinct Effects of delta-9-Tetrahydrocannabinol and Cannabidiol on Neural Activation During Emotional Processing. Arch Gen Psychiatry, 66(1):95-105.

The above study is interesting because it shows that THC produces anxiogenic effects (makes you anxious) but that CBD (cannabidiol) is anxiolytic (reduces anxiety). This explains why users feel both relaxed when high and progressively develop symptoms of anxiety:

1. Troisi A, Pasini A, Saracco M, Spalletta G. Psychiatric symptoms in male cannabis users not using other illicit drugs. Addiction. 1998;93(4):487-492. FULL TEXT | WEB OF SCIENCE | PUBMED
2. Reilly D, Didcott P, Swift W, Hall W. Long-term cannabis use: characteristics of users in an Australian rural area. Addiction. 1998;93(6):837-846. FULL TEXT | WEB OF SCIENCE | PUBMED
3. Clough AR, d'Abbs P, Cairney S, Gray D, Maruff P, Parker R, O’Reilly B. Adverse mental health effects of cannabis use in two indigenous communities in Arnhem Land, Northern Territory, Australia: exploratory study. Aust N Z J Psychiatry. 2005;39(7):612-620. FULL TEXT | WEB OF SCIENCE | PUBMED
4. Feeney GF, Connor JP, Young RM, Tucker J, McPherson A. Cannabis dependence and mental health perception amongst people diverted by police after arrest for cannabis-related offending behaviour in Australia. Crim Behav Ment Health. 2005;15(4):249-260. FULL TEXT | PUBMED
5. Zvolensky MJ, Bernstein A, Sachs-Ericsson N, Schmidt NB, Buckner JD, Bonn-Miller MO. Lifetime associations between cannabis, use, abuse, and dependence and panic attacks in a representative sample. J Psychiatr Res. 2006;40(6):477-486. FULL TEXT | WEB OF SCIENCE | PUBMED
6. Fergusson DM, Horwood LJ. Early onset cannabis use and psychosocial adjustment in young adults. Addiction. 1997;92(3):279-296. FULL TEXT | WEB OF SCIENCE | PUBMED
7. Agosti V, Nunes E, Levin F. Rates of psychiatric comorbidity among US residents with lifetime cannabis dependence. Am J Drug Alcohol Abuse. 2002;28(4):643-652. FULL TEXT | PUBMED
8. Swadi H, Bobier C. Substance use disorder comorbidity among inpatient youths with psychiatric disorder. Aust N Z J Psychiatry. 2003;37(3):294-298. FULL TEXT | WEB OF SCIENCE | PUBMED

The problem with this is that over the last 20-30 years, the level of THC, on average, has been bred to increase from 5-7% in the 1970s to current levels of 20-30% in the strongest weed available. The result has been a serious increase in psychotic and other mental health issues in users, especially adolescents and teens.

Bottom line: Cognitive dysfunction associated with long-term or heavy cannabis use is similar in many respects to the cognitive endophenotypes that have been proposed as vulnerability markers of schizophrenia.

Citation for the article below:
University of Bristol. (2011, October 27). "How Cannabis Causes 'Cognitive Chaos' In The Brain." Medical News Today. Retrieved from http://www.medicalnewstoday.com/releases/236616.php.

How Cannabis Causes 'Cognitive Chaos' In The Brain

Cannabis use is associated with disturbances in concentration and memory. New research by neuroscientists at the University of Bristol, published in the Journal of Neuroscience [Oct. 25], has found that brain activity becomes uncoordinated and inaccurate during these altered states of mind, leading to neurophysiological and behavioural impairments reminiscent of those seen in schizophrenia. 


The collaborative study, led by Dr Matt Jones from the University's School of Physiology and Pharmacology, tested whether the detrimental effects of cannabis on memory and cognition could be the result of 'disorchestrated' brain networks.


Brain activity can be compared to performance of a philharmonic orchestra in which string, brass, woodwind and percussion sections are coupled together in rhythms dictated by the conductor. Similarly, specific structures in the brain tune in to one another at defined frequencies: their rhythmic activity gives rise to brain waves, and the tuning of these brain waves normally allows processing of information used to guide our behaviour.


Using state-of-the-art technology, the researchers measured electrical activity from hundreds of neurons in rats that were given a drug that mimics the psychoactive ingredient of marijuana. While the effects of the drug on individual brain regions were subtle, the drug completely disrupted co-ordinated brain waves across the hippocampus and prefrontal cortex, as though two sections of the orchestra were playing out of synch.


Both these brain structures are essential for memory and decision-making and heavily implicated in the pathology of schizophrenia.


The results from the study show that as a consequence of this decoupling of hippocampus and prefrontal cortex, the rats became unable to make accurate decisions when navigating around a maze.


Dr Jones, lead author and MRC Senior Non-clinical Fellow at the University, said: "Marijuana abuse is common among sufferers of schizophrenia and recent studies have shown that the psychoactive ingredient of marijuana can induce some symptoms of schizophrenia in healthy volunteers. These findings are therefore important for our understanding of psychiatric diseases, which may arise as a consequence of 'disorchestrated brains' and could be treated by re-tuning brain activity."


Michal Kucewicz, first author on the study, added: "These results are an important step forward in our understanding of how rhythmic activity in the brain underlies thought processes in health and disease."


The research is part of a Medical Research Council (MRC)-supported collaboration between the University and the Eli Lilly & Co. Centre for Cognitive Neuroscience that aims to develop new tools and targets for treatment of brain diseases like schizophrenia and Alzheimer's disease.