Legalise it? The real dangers of cannabis are not to be ignored

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  • Looks can be deceiving: an employee displays recreational marijuana inside a dispensary in Colorado (Photograph by Matthew Staver/The Washington Post)

    Looks can be deceiving: an employee displays recreational marijuana inside a dispensary in Colorado (Photograph by Matthew Staver/The Washington Post)


Three decades ago, I would have been over the moon to see cannabis legalised. It would have saved me a lot of effort spent trying to avoid detection, constantly looking for places to hide a joint. I smoked throughout my teens and early twenties. During this period, upon landing in a new city, my first order of business was to score a quarter-ounce. The thought of a concert or a vacation without weed was simply too bleak.

These days it is hard to find anyone critical of cannabis. The drug enjoys broad acceptance by most Americans — 63 per cent favoured ending cannabis prohibition in a recent Quinnipiac poll — and legislators on both sides of the aisle are becoming more likely to endorse than condemn it.

After years of loosening restrictions on the state level, there are signs that the federal government could follow suit: in April, Senate Minority Leader Charles Schumer, the Democrat from New York, became the first leader of either party to support decriminalising cannabis at the federal level, and Donald Trump — his attorney-general notwithstanding — promised a Republican senator from Colorado that he would protect states that have legalised pot.

And why not? The drug is widely thought to be either benign or beneficial. Even many of those apathetic towards its potential health benefits are ecstatic about its commercial appeal, whether for personal profit or state tax revenue.

Legalisation in many cases, and for many reasons, can be a good thing. I’m sympathetic. But I am also a neuroscientist, and I can see that the story is being oversimplified.

The debate around legalisation, which often focuses on the history of racist drug laws and their selective enforcement, is astoundingly naive about how the widespread use of pot will affect communities and individuals, particularly teenagers.

In our rush to throw open the gate, we might want to pause to consider how well the political movement matches up with the science, which is producing inconveniently alarming studies about what pot does to the adolescent brain.

I took a backdoor route to the science of cannabis, starting with a personal investigation of the plant’s effects. When I was growing up in South Florida in the 1980s, pot was readily available, and my appreciation quickly formed the basis for an avid habit. Weed seemed an antidote to my adolescent angst and ennui, without the sloppiness of alcohol or the jaw-grinding intensity of stimulants.

Of the many things I loved about getting high, the one I loved best was that it commuted the voice in my head — usually peevish or bored — to one full of curiosity and delight.

Cannabis transformed the mundane into something dramatic: family outings, school, work or just sitting on the couch became endlessly entertaining when I was stoned.

Like any mind-altering substance, cannabis produces its effects by changing the rate of what is already going on in the brain.

In this case, the active ingredient delta-9-THC substitutes for your own natural endocannabinoids and mimics their effects. It activates the same chemical processes the brain employs to modulate thoughts, emotions and experiences.

These specific neurotransmitters, used in a targeted and judicious way, help us to sort the relentless stream of inputs and flag the ones that should stand out from the torrent of neural activity coding stray thoughts, urges and experience.

By flooding the entire brain, as opposed to select synapses, cannabis can make everything, including the most boring activities, take on a sparkling transcendence.

Why object to this enhancement? As one new father told me, imbibing made caring for his toddler much more engrossing and thus made him, he thought, a better parent.

There are two important caveats from a neurobiological perspective. As watering a flooded field is moot, widespread cannabinoid activity, by highlighting everything, conveys nothing. And amid the flood induced by regular cannabis use, the brain dampens its intrinsic machinery to compensate for excessive stimulation.

Chronic exposure ultimately impairs our ability to imbue value or importance to experiences that truly warrant it.

In adults, such neuro-adjustment may hamper or derail a successful and otherwise fulfilling life, although these capacities will probably recover with abstinence. But the consequences of this desensitisation are more profound, perhaps even permanent, for adolescent brains.

Adolescence is a critical period of development, when brain cells are primed to undergo significant organisational changes: some neural connections are proliferating and strengthening, while others are pared away.

Although studies have not found that legalising or decriminalising cannabis leads to increased use among adolescents, perhaps this is because it is already so popular.

More teenagers now smoke cannabis than smoke products with nicotine; between 30 per cent and 40 per cent of high school seniors report smoking pot in the past year, about 20 per cent got high in the past month, and about 6 per cent admit to using virtually every day.

The potential consequences are unlikely to be rare or trivial.

The decade or so between puberty and brain maturation is a critical period of enhanced sensitivity to internal and external stimuli.

Noticing and appreciating new ideas and experiences helps teens to develop a sense of personal identity that will influence vocational, romantic and other decisions — and guide their life’s trajectory.

Although a boring life is undoubtedly more tolerable when high, with repeated use of cannabis, natural stimuli, such as those associated with goals or relationships, are unlikely to be as compelling.

It is not surprising, then, that heavy-smoking teens who show evidence of reduced activity in brain circuits critical for flagging newsworthy experiences are 60 per cent less likely to graduate from high school, and are at substantially increased risk for heroin addiction and alcoholism.

They show alterations in cortical structures associated with impulsivity and negative moods; they are seven times more likely to attempt suicide.

Recent data is even more alarming: the offspring of partying adolescents, specifically those who used THC, may be at increased risk for mental illness and addiction as a result of changes to the epigenome — even if those children are years away from being conceived. The epigenome is a record of molecular imprints of potent experiences, including cannabis exposure, that lead to persistent changes in gene expression and behaviour, even across generations. Although the critical studies are only now beginning, many neuroscientists prophesy a social version of Rachel Carson’s Silent Spring, in which we learn we have burdened our heirs only generations hence.

Might the relationship between cannabis exposure and changes in brain and behaviour be coincidence, as tobacco companies asserted about the link between cancer and smoking, or does THC cause these effects? Unfortunately, we can’t assign people to smoking and non-smoking groups in experiments, but efforts are under way to follow a large sample of children across the course of adolescent development to study the effects of drug exposure, along with a host of other factors, on brain structure and function, so future studies will probably be able to answer this question.

In the same way someone who habitually increases the volume in their headphones reduces their sensitivity to birdsong, I followed the “gateway” pattern from pot and alcohol to harder drugs, leaping into the undertow that eventually swept away much of what mattered in my life. I began and ended each day with the bong on my nightstand as I floundered in school, at work and in my relationships. It took years of abstinence, probably mirroring the duration and intensity of my exposure, but my motivation for adventure seems largely restored. I’ve been sober since 1986 and went on to become a teacher and scholar. The single-mindedness I once directed towards getting high came in handy as I worked on my dissertation. I suspect, though, that my pharmacologic adventures left their mark.

Now, as a scientist, I’m unimpressed with many of the widely used arguments for the legalisation of cannabis.

“It’s natural!” So is arsenic.

“It’s beneficial!” The best-documented medicinal effects of cannabis are achieved without the chemical compound that gets users high.

“It’s not addictive!” This is false, because the brain adapts to cannabis as it does to all abused drugs, and these neural adjustments lead to tolerance, dependence and craving — the hallmarks of addiction.

It’s true that a lack of benefit, or even a risk for addiction, has not stopped other drugs such as alcohol or nicotine from being legal, used and abused. The long American history of legislative hypocrisy and selective enforcement surrounding mind-altering substances is plain to see. The Marihuana Tax Act of 1937, the first legislation designed to regulate pot, was passed amid anti-Mexican sentiment — as well as efforts to restrict cultivation of hemp, which threatened timber production. It had nothing do with scientific evidence of harm. That is true of most drug legislation in the United States. Were it not the case, LSD would be less regulated than alcohol, since the health, economic and social costs of the latter far outweigh those of the former. (Most neuroscientists don’t believe that LSD is addictive; its potential benefits are being studied at Johns Hopkins and New York University, among other places.)

Still, I’m not against legalisation. I simply object to the astounding lack of scepticism about pot in our present debate. Whether or not to legalise weed is the wrong question. The right one is: how will growing use of delta-9-THC affect individuals and communities?

Although the evidence is far from complete, wishful thinking and widespread enthusiasm are no substitutes for careful consideration. Instead of rushing to enact new laws that are as nonsensical as the ones they replace, let’s sort out the costs and benefits, using existing scientific knowledge, while supporting the research needed to clarify the neural and social consequences of frequent use of THC. Perhaps then we will avoid practices that inure future generations to what’s really important.

Judith Grisel is a professor of psychology and neuroscience at Bucknell University, where she is a practising neuroscientist

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Published May 28, 2018 at 8:00 am (Updated May 27, 2018 at 8:00 pm)

Legalise it? The real dangers of cannabis are not to be ignored

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