There are two things that are certain about marijuana. The first is that it doesn’t discriminate, attaching itself to all different lives – fortunate, unfortunate, happy, sad, educated, wealthy, poor. The second is that whatever the life it attaches to, marijuana will do damage if it stays.

It has been proven beyond doubt that frequent marijuana use damages the brains of teenagers and young adults.

Throughout adolescence and into the mid-20s, the brain continues to develop in ways that are critical for higher-order thinking and executive functioning (memory, reasoning, problem solving). White matter, which is important for neural efficiency, increases in quality and volume into the early 30s.

Given that adolescence is such an important developmental period for the brain, exposure to drugs during this time has a greater impact on the brain than it does during adulthood.

Psychologists have noted the effects to include cognitive decline, poor attention and memory and diminished IQ.

‘It needs to be emphasised that regular cannabis use, which we consider once a week, is not safe and may result in addiction and neurocognitive damage, especially in youth.’ Dr Krista Lisdahl, a director of the brain imaging and neuropsychology lab at University of Wisconsin-Milwaukee.

In a 2012 longitudinal study of 1037 participants who were followed from birth to age 38, it was found that those who regularly used marijuana lost on average of 5.8 IQ points by the time they reach adulthood. This was compared to those who never regularly used marijuana whose IQ slightly increased by 0.8 IQ points from childhood to adulthood.

The physiological evidence is clear.

Brain scans of regular marijuana users show significant structural changes including abnormalities in the brain’s gray matter. These abnormalities are associated with reduced cognitive function, increased mood symptoms and poor memory. These changes have been found in users as young as 16 and were not related to major medical conditions, prenatal drug exposure, developmental delays and learning disabilities.

These findings are not intended to push against the legalisation of marijuana for medicinal purposes. Rather, it should highlight the need to implement stringent conditions on access.

‘When considering legalization, policymakers need to address ways to prevent easy access to marijuana and provide additional treatment funding for adolescent and young adult users,’ Lisdahl explained.

In considering legalisation of the marijuana, weight also needs to be given to regulating the levels of psychoactivetetrahydrocannabinol (THC – the chemical responsible for the majority of marijuana’s psychological effects) to reduce the potential neurocognitive effects.

There is research evidence that has linked frequent use of high levels of THC to depression, anxiety and psychosis.

According to Dr Alan Budney of the Department of Psychiatry at Geisel School of Medicine at Dartmouth, ‘Recent studies suggest that this relationship between marijuana and mental illness may be moderated by how often marijuana is used and potency of the substance. Unfortunately, much of what we know from earlier research is based on smoking marijuana with much lower doses of THC than are commonly used today.’

In a 2013 study of over 17,482 teenagers, marijuana use was found to be higher among teenagers from countries that had a more accepting attitude towards medical marijuana. Greater tolerance of marijuana for medicinal purposes seems to promote a greater tolerance for the drug generally, at least by adolescents, possibly because of a diminished perception of the risks associated with the drug.

The risks of marijuana on the developing brain have been extensively documented. The debate around the legalisation of marijuana for medicinal purposes is in full swing. Should this end on medicinal marijuana being approved, research points to the importance of consideration being given to restricting access, reducing the potency of THC and raising awareness, particularly in adolescents, on the risks of recreational use.

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