Marijuana May Both Trigger and Suppress Psychosis

Researchers uncover connections between marijuana and the psychoses of schizophrenia

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It’s a familiar experience for most marijuana smokers — that sudden discovery of great meaning, humor or intensity in what they would ordinarily find to be mundane situations and sensations. It’s part of why people seek out marijuana, but this undue attention to what usually seems insignificant is also part of the psychotic experience of schizophrenia — and new research finds that the two main ingredients in marijuana have opposing effects on it.

The study examined 15 normal men who had previously smoked cannabis only a few times. Researchers exposed the men to each of the two most psychoactive ingredients in marijuana — delta-9 tetrahydrocannabinol (THC) and cannabidiol (CBD) and compared their effects with those of a placebo while the participants performed a mental task.

The men were asked to study arrows, placed on either the left or the right of the screen, which mostly pointed straight but occasionally — in what’s known as the “oddball” situation — the arrows were tilted at a 23-degree angle. The participants’ brains were scanned while they identified which direction the arrows were pointing in, so scientists could determine which parts of the brain were affected by marijuana’s active ingredients.

In all of the situations, not surprisingly, it took longer for the men to respond to the unusually pointing arrows. After taking THC, however, the men responded faster in both the oddball and usual cases than they did under the influence of either CBD or the placebo. But their responses were even more affected in the usual cases.

The fact that that the men, after taking THC, responded even faster to the straight arrows than to the bent ones meant that THC particularly affected how participants experienced familiar sights. (Interestingly, while THC seemed to reduce the accuracy of responses, compared with CBD and the placebo, the difference was not statistically significant, meaning it could have been due to chance.)

MORE: Why Pot Smokers Are Paranoid

The scans showed that THC lowered activity in a region on the right side of the brain called the caudate nucleus — and the more it reduced activation, the greater effect it had on the men’s response times and the more they experienced a sense of paranoia and an intensified sense of significance and auditory hallucinations.

Those are all psychotic symptoms that can indicate schizophrenia if they occur when people are not high on marijuana or other drugs. Understanding how they occur may help researchers better understand how psychosis develops. For example, an inability to filter out irrelevant stimuli may lead people to hallucinate voices when others hear only noise.  And if a sense of heightened significance occurs simultaneously, this could lead to hallucinations common in schizophrenia, like a sense that the voices are commanding you to do something important or are the voices of religious authorities or gods.

Of course, the same lack of filtering — with less intensity or with awareness that they are produced by a drug — could also aid creativity, which often involves paying attention to those elements of life that are usually ignored. Indeed, some research suggests that the relatives of people with schizophrenia are more creative than others — and this tendency not to tune out the ordinary could explain why.

In contrast, CBD had the opposite effect on the brain; earlier research suggested that it may have antipsychotic properties.

Does that mean marijuana could play a role in both triggering and even treating schizophrenia? Possibly. In people with the disorder, marijuana use can intensify symptoms, and research suggests it can bring on schizophrenia in some people who are predisposed to develop it. But the interaction is complicated: as marijuana use has increased dramatically in the population, schizophrenia rates have stayed the same.

MORE: Marijuana Linked with Earlier Onset of Schizophrenia in Research Review

CBD might help explain that. Since marijuana typically contains both compounds, CBD could counteract THC’s tendency to create psychotic symptoms, which might prevent a pot smoker with a predisposition to schizophrenia from falling over the edge into active disease.

And if this is true — as studies increasingly suggest is the case — it may have important implications for the debates over both marijuana legalization and “fake pot” products like Spice and K2. These contain only THC-like substances and therefore may actually be more dangerous than natural weed.  If marijuana and similar substances were regulated, a requirement to include a certain level of CBD might be one way to minimize harm.

MORE: A Complex Link Between Marijuana and Schizophrenia

The research was published in the Archives of General Psychiatry and led by Sagnik Bhattacharyya of the Department of Psychosis studies at King’s College, London.

Maia Szalavitz is a health writer for Find her on Twitter at @maiasz. You can also continue the discussion on TIME Healthland‘s Facebook page and on Twitter at @TIMEHealthland.