Smoking high-strength cannabis may injury nerve fibers in brain

Study suggests high levels of skunk use may affect the brains white matter, attaining communication between the right and left hemispheres less efficient

High-strength cannabis may injury nerve fibers that handle the flow of messages across the two halves of the brain, scientists claim. Brain scans of people who regularly smoked strong skunk-like cannabis revealed subtle differences in the white matter that connects the left and right hemispheres and carries signals from one side of the brain to the other.

The changes were not seen in those who never employed cannabis or smoked only the less potent forms of the narcotic, the researchers found.

The study is thought to be the first to look at the effects of cannabis effectivenes on brain structure, and been shown that greater use of skunk may cause more damage to the corpus callosum, attaining communications across the brains hemispheres less efficient.

Paola Dazzan, a neurobiologist at the Institute of Psychiatry at Kings College London, said the effects appeared to be linked to the level of active ingredient, tetrahydrocannabinol( THC ), in cannabis. While traditional different forms of cannabis contain 2 to 4% THC, the more potent assortments( of which there are about 100 ), can contain 10 to 14% THC, according to the DrugScope charity.

If you look at the corpus callosum, what were seeing is a significant difference in the white matter between those who use high effectivenes cannabis and those who never use the narcotic, or use the low-potency narcotic, said Dazzan. The corpus callosum is rich in cannabinoid receptors, on which the THC chemical acts.

A DTI image of the corpus callosum, as seen from the side, demonstrated by red on and superimposed on a background MRI image of the brain. Photograph: Institute of Psychiatry

The difference is there whether you have psychosis or not, and we think this is strictly related to the effectivenes of the cannabis, she added. Details of the study are reported in the journal Psychological Medicine.

The researchers employed two scanning techniques, magnetic resonance imaging( MRI) and diffusion tensor imaging( DTI ), to examine the corpus callosum, the largest region of white matter, in the brains of 56 patients who had reported a first episode of psychosis, and 43 healthy volunteers from the local community.

The scans found that daily users of high-potency cannabis had a slightly greater by about 2% mean diffusivity in the corpus callosum. That reflects a problem in the white matter that is likely attains it least efficient, Dazzan told the Guardian. We dont know exactly what it means for the person or persons, but it suggests there is less efficient transfer of information.

The study cannot confirm that high levels of THC in cannabis cause changes to white matter. As Dazzan notes, it is may be that people with injury white matter are more likely to smoke skunk in the first place.

It is possible that these people already have a different brain and they are more likely to use cannabis. But what we can say is if its high effectivenes, and if you smoke frequently, your brain is different from the brain of someone who smokes normal cannabis, and from someone who doesnt smoke cannabis at all, she said.

But even with the uncertainty over cause and effect, she exhorted users and public health workers to change how they think about cannabis use. When it comes to alcohol, we are used to thinking about how much people drink, and whether they are drinking wine, brew, or whisky. We should think of cannabis in a similar way, in terms of THC and the different contents cannabis can have, and potentially the effects on health will be different, she said.

As we have suggested previously, when assessing cannabis use, it is extremely important to gather information on how often and what type of cannabis is being used. These details can help quantify health risks of mental health problems and increase awareness of the type of damage these substances can do to the brain, she added.

In February, Dazzan and others at the Institute of Psychiatry reported that the ready accessibility of skunk in south London might be behind a rise in the proportion of new cases of psychosis being attributed to cannabis.

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