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The Research Institute for Health and Social Change, MMU
The cannabis connection
Researchers in the Psychology Department at Manchester Metropolitan University (MMU) are researching the relationship between cannabis and mental illness. They are looking for anyone over the age of 18, who has a history of mental health problems and who has used cannabis at least once to complete an anonymous questionnaire.
At this time they are only interested in the recreational (or non-medically prescribed) use of natural (non-synthetic) cannabis products. If you have ONLY had experience of synthetic cannabis products (e.g. Spice), or medically prescribed natural cannabis products (e.g. Sativex) you would not be eligible to take part.
It has been hypothesised that cannabis (along with other naturally occurring psychoactive compounds) acted as a catalyst in human evolution , with evidence for this theory derived from the presence of sites specifically for the binding of cannabanoids, the CB1 and CB2 receptors .
However, at this current moment in time there is only limited evidence and available data to this effect. Even if there is not a causal relationship between modern humans and cannabis there is definitely an ancient one. Cannabis has been used both in ancient and modern societies as an aid for meditation and religious ceremony. 
Records suggest that cannabis has been used as a medicine, and for recreational purposes for many thousands of years  .The medicinally, established beneficial effects include pain relief , reduced anxiety , and a marked reduction in the tendency to feel [or be] physically sick .
Recreationally, cannabis induces a number of (pleasant) experiences including euphoria, feelings of enhanced creativity, and feelings of enhanced perception which can lead to a greater appreciation for music and imagery.
Unfortunately, the drug can also induce unpleasant effects; variously described as 'aversive' 'negative' and/or 'dysphoric'. In some otherwise healthy individuals, cannabis (especially in larger quantities) induces a type of psychotic state that has been likened to acute schizophrenia.
These psychotic states are characterised by perceptual disturbances (seeing, hearing and experiencing things others cannot), delusions (having firmly held yet false beliefs), and paranoia. Although these changes are usually short-lived, there is increasing concern that some people are particularly sensitive to these 'negative' effects, and there is currently a debate as to whether cannabis can actually cause schizophrenia or other forms of long term (chronic) psychosis in such vulnerable individuals.
Cannabis and mental illness: cause or effect?
Cannabis is widely used by people with an existing diagnosis of schizophrenia or some related form of psychosis , and research has suggested that its use may lead to an increased risk of further relapses in a dose-dependent fashion;  the more you use the more likely you are to experience further bouts of illness. However, this does not necessarily mean cannabis causes schizophrenia per se: For example, it is possible that a young person who may go on to develop schizophrenia as an adult, is also more inclined to use cannabis, perhaps because of their personality, or as an expression of their openness to unusual experiences.
It is also the case that some people with a history of psychotic illness say they use cannabis as a form of self-medication (to treat their illness); or to counter the unpleasant effects of their conventional anti-psychotic meds.
Despite lots of research linking cannabis and schizophrenia, it is very difficult to produce conclusive scientific evidence that cannabis causes schizophrenia in people who otherwise would not develop it. All we can say at the moment is that some people appear to be particularly susceptible to the unpleasant effects of the drug, and perhaps that these individuals are at greater risk of subsequent illness, especially if they also have a predisposition to, or family history of, psychiatric disorder.
The effects of cannabis
Cannabis is a very diverse substance, typically containing over 70 psychoactive (mind-affecting) chemicals; the two main ones being THC and CBD . Research has shown that pure THC given to people with no history of mental illness can produce short-lived psychosis-like states .
THC increases dopamine release in the brain , and can make some of the symptoms associated with schizophrenia worse . Incidentally, most anti-psychotic meds are thought to reduce symptoms by damping down the same dopamine system , and these meds also limit the ability of THC to induce psychotic-like states .
On the other hand CBD, which is the second most abundant chemical in cannabis, has been shown to relieve anxiety 6 and feasibly improve mood , and there is even evidence that it may possess anti-psychotic properties .
In other words, the two most abundant active components of cannabis appear to have opposite effects (which may explain the range of reported experiences, positive and negative, associated with its use).
Advancement in botanical techniques and selective breeding has resulted in a change in the chemical make-up of cannabis most commonly available . Varieties of high potency 'skunk', which contains proportionately more THC and less CBD have certainly become more popular , meaning that the type of cannabis most commonly used is potentially worse for a person's mental health than was the case in the past. This has led some experts to predict a significant rise in the coming years, in the number of individuals seeking/requiring help for cannabis-induced (or cannabis-complicated) psychotic conditions.
We share these concerns: However, our research on the psychological effects of cannabis, conducted over the past 7+ years on over 1000 non-clinical respondents, and reported in several scientific journals , , , [23, , has led us to the view that most people can use cannabis with little risk ]of severe mental illness. However, a relatively small proportion of users, with a so-called 'high schizotypy' personality profile (characterised by a willingness to adopt irrational beliefs, susceptibility to perceptual disturbances and poor interpersonal social skills) are at increased risk of experiencing proportionately fewer positive and more negative effects of the drug. We believe that such individuals may, through continued use of cannabis, be putting themselves at increased risk of later mental illness.
Cannabis; your experiences and your health
About 2/3 of young adults have used, or currently use, cannabis, yet only 1 or 2 in 100 develops a functional psychotic disorder. We have the idea that particular cannabis induced experiences might serve as 'danger-signs' of later mental health problems for a particular subset of 'vulnerable' individuals. Now to test this properly we would need to follow-up a massive sample of people for many years but we simply do not have the necessary resources for such a project. However, an alternative approach is to record cannabis experiences in individuals with existing mental health problems, and this is where you come in!
Essentially, we want to see if people with ongoing problems, who have also used (and may continue to use) cannabis, have the same or similar reactions to the drug as people without a history of mental health problems, and if not, how their responses differ.
A very important outcome of our proposed research is the identification of cannabis-induced experiences that could predict increased proneness to subsequent psychosis in currently 'healthy' individuals, and your involvement in our study could help us achieve this goal!
To take part we do not need your name or contact details, in fact you can take part completely anonymously. To participate or just for a bit of further information please go to our website <click here> or alternatively you can contact Rohan Morris
phone on 0161 247 2415
Rohan Morris RIHSC / Department of Psychology Elizabeth Gaskell Manchester Metropolitan University Hathersage Road M13 OJA
22 Drake, R. J., Barkus, E., Stirling, J., Morris, R. & Lewis, S. (2011). Multidimensional scaling of relationships between experiences due to cannabis. International Congress on Schizophrenia Research, Colorado