1. Many potential "psychosis-risk" persons are likely to attempt self-medication with cannabis long before the first "episode" when their condition gets attention, thus a falso conclusion results that cannabis, or especially high THC-cannabis, caused the malady. American readers may not be aware that an estimated 2/3 of all cannabis users in the UK mix cannabis in a joint with tobackgo (summary does not say if this possible adverse synergy was taken note of in the recent study). There is also no mention of the fact that, once using cannabis, a person enters a new life-condition of being in danger of arrest, prosecution and social blacklisting, and that this is what evokes the psychosis.

One could also speculate that those with a more-severe mental illness such as schizophrenia might be attracted to the more-potent version simply because it more effectively medicates their psychotic symptoms.

This appears to be irresponsible and flawed research. Approximately 50% of tobacco is sold to people with a mental health diagnosis in the United States, does this mean tobacco causes mental health problems? Why not publish the research so people and review the data and draw their own conclusions?

Slow done on the defensiveness Barry- your bias is showing. I see the use of the conditional word "could" in the first sentence of this summary that is the hallmark of such research. A correlation between two events does not prove causation (and if you have a master's degree you already know that)! It merely suggests that further research is warranted. Both hypotheses are valid; that is, use of high THC marijuana may cause individuals who are predisposed to developing psychoses to experience psychotic symptoms (kindling effect) or as suggested by maxwood and Kevin, individuals who are predisposed to psychoses use high THC marijuana to alleviate (self-medicate)their symptoms. BTW, this isn't news as the potential link between schizophrenia and THC use has been previously reported by other researchers. If the results of the research are used as a propaganda tool (ala Reefer Madness), then you've got something to complain about; however, if this info is used to spur physicians to begin to screen their patients re: habitual substance abuse and follow that up with further mental health screening, many mental illnesses could be detected earlier and perhaps inpatient hospitalizations wouldn't be the first indication that something is seriously amiss.

Right on William W! What were the ages of individuals who experienced Psychosis? Were they predisposed to Mental illness? ..and the control group, age, predispositions? Individuals who have schizophrenia usually have their first psychotic break in their late teens to early 20s. Anyone who is predisposed or dx'd w/ mental illness may exacerbate or medicate their illness w/ certain drugs. This is not news and those of us who work w/ pt's who are dually dx'd face this daily.

Hang on. There is a fundamental misunderstanding here. The "potency" of the cannabis is being mentioned as a contributing factor. What is not being mentioned is that cannabis users will consume more or less till they attain the desired effect. Higher "potency" just means less is needed, it does not mean the effect is somehow more pronounced or intense. This is a constant problem when the prejudicial term "higher potency" is used. Effects are tied to dosage, not so called "potency". All pharmaceutical psycho active drugs have side effects of some kind. The attempt to pin a negative side effect on cannabis as if that is enough to justify prohibition is dishonest.

Does no one here question the fact the US Govt promotes the use of 100% THC in the form of marinol every time they say "you don't need raw marijuana for medicine -- there is a pill you can take!" The shills of this propaganda about the "new" the dangers of so-called high THC "skunk" are whistling in the wind.

May I recommend everyone read the article for themselves. It is readily available online. Having read the original research this is a well-done study that adds weight to an issue no longer in much dispute at least in the research community, marijuana is linked to psychosis problems. The Lancet (a prominent British medical journal)recently withdrew its 1995 statement that marijuana use was harmless because of this issue. This study was well done.

As to some of the specific objections noted above: The original article cannot be printed here, it is copyrighted, but you can read with a small investment of time and money ($12). The psychosis cases and the control group were well-matched, with no statistical differences in age, gender, ethnicity, educational level, etc. In fact, the percentage of THC users in the control group was actually higher than in the study group, meaning the findings were, if anything, weakened and they were still significant. Other research has found that while users do adjust their dose, some people--notably young adult males--actually increase their use when they encounter high-potency. (Korf et al., 2007, Internation Journal of Drug Policy) This study gives weight to a dose-response relationship between marijuana and psychosis. The more people smoke and the higher the potency they dose, the more likely they were to have experienced a significant psychosis episode requiring hospitalization. This is the primary finding of this study. Please, before you criticize the research, read it. And finally, no one who was around in the 70's failed to know that using marijuana could make you paranoid, which is, in fact, one symptom of psychosis.