Harvard Medical School professor Dr Bertha Madras has spent nearly four decades revolutionising how we understand addiction neuroscience. Her recent conversation on the Unnecessary Harm Podcast delivered findings that should alarm every parent, educator, and policymaker: substances don’t just impair the brain. They destroy it.
But here’s the critical insight. Substance use disorders are the only class of brain diseases we can prevent 100%. The question is whether we’re willing to build the right brain defence against drugs, starting where it matters most: in families.
The Permanent Damage You Can’t See
Dr Madras’s laboratory research at McLean Hospital has uncovered something disturbing about methamphetamine. It doesn’t just alter brain chemistry. It kills nerve cells permanently.
“Methamphetamine literally destroys certain nerve cells,” Dr Madras explained. “That’s not even a disease process. That’s death. Pure death.”
Cocaine changes the brain’s vascularisation to the point where parts of the brain simply don’t receive enough oxygen. Opioids, during an overdose, cut oxygen supply through slowed breathing and reduced heart rate. The result? Between 10,000 and 100,000 nerve cells die, and they never regenerate.
Alcohol damages brain tissue through toxic exposure. Ketamine at high doses causes cellular death. These aren’t temporary impairments that resolve once someone stops using. This is permanent neurological damage occurring at the cellular level. Any serious approach to brain defence against drugs must acknowledge this harsh reality: some damage cannot be undone.
For young people, the stakes are even higher. The earlier someone begins using substances, the more likely they are to develop an addiction. This holds true across every major drug category: alcohol, nicotine, opioids, cannabis, cocaine, MDMA, and amphetamines.
Cannabis: The 1,000 Gene Problem
Dr Madras’s laboratory recently revealed alarming effects of daily cannabis use in adolescents. Her team administered moderate daily doses of THC to non-human primates (because ethical constraints prevent such studies in human teenagers) and observed profound inflammatory changes in the amygdala.
This brain region controls mood, affect, depression, suicidality, sleep patterns, learning, memory, and plays a role in psychosis. The amygdala is also packed with cannabinoid receptors and is critical for adolescent brain development.
“We were stunned to see these data,” Dr Madras said. “I was so shocked that I had it done in three different places at MIT, Harvard, and the University of Toronto. We all confirmed it.”
The second finding was even more disturbing. Daily THC exposure altered the expression of over 1,000 genes in the same brain area. This represents epigenetic change at a massive scale, the kind of biological reprogramming that has lasting consequences.
These findings challenge the myth that cannabis is harmless, especially for young people. The cannabis available today is vastly different from what previous generations used. It has been heavily engineered for higher potency, making it misleading to describe it as a purely “natural” substance.
Brain Defence: The Schizophrenia Risk Nobody Wants to Discuss
If you show up in an emergency department with psychosis after recently using potent cannabis, research shows you have a 35 to 60% probability of that psychosis converting to schizophrenia. That’s not a temporary mental health episode. That’s a lifelong disorder that’s difficult to treat and difficult to live with.
Dr Madras addressed the “correlation versus causation” argument head-on, pointing to the Bradford Hill criteria that distinguish between the two. Cannabis use meets multiple criteria for causation:
There’s a dose-response function. The more you use, the higher your risk. The pattern appears across seven different countries, ruling out cultural or societal factors. Earlier age of onset dramatically increases risk. The further away in time from when someone stopped using cannabis, the lower their risk of developing schizophrenia.
“After looking at all these criteria, I find more and more psychiatrists willing to accept the fact that it’s a component cause, not a correlation, but a component cause of schizophrenia,” Dr Madras stated.
In Ontario, Canada, new schizophrenia cases associated with cannabis use disorder jumped from 1.6% in 2006 to 9.6% in 2022. That data was published in JAMA Network Open, one of the most rigorous medical journals in the world.
Perhaps most significantly, research suggests that if people did not become addicted to cannabis, schizophrenia cases could be reduced by 25 to 30%, with higher rates in males than females.
Why Young Brains Are Uniquely Vulnerable
Adolescence represents one of two age groups with the greatest vulnerability to substances (the other being developing foetuses). When young people begin using drugs, several devastating processes unfold simultaneously. Understanding brain defence against drugs means recognising these vulnerabilities before they become lifelong problems.
First, substances interfere with learning and memory, derailing academic achievement. Second, they disrupt goal-directed behaviours and motivation, the very capacities teenagers need to develop into functional adults. Third, and perhaps most intriguing, early substance use can cause arrested development.
Dr Madras described meeting a man in his 40s who was in treatment for opioid addiction. Despite being dapper and sophisticated in appearance, his great pleasure in life was teaching young people how to inject drugs properly. “It sounded like a 13-year-old kid trying to teach his friends how to throw a baseball,” she observed.
This arrested development means someone who begins using at 12, 14, or 15 and develops daily use with addiction may reach 40 or 50 without having gone through the normal developmental stages that non-users experience. They’re trapped in an adolescent mentality, unable to develop the emotional regulation, delayed gratification, and personal responsibility that mark adulthood.
The Adolescent Brain Cognitive Development Study, which is following over 12,000 young people from age nine onwards, will eventually provide longitudinal data on exactly what happens to those who begin using substances early. But we don’t need to wait for complete results to understand the trajectory. The evidence is already clear.
Brain Defence Begins at Home
Dr Madras’s research has identified something that cuts through all the complexity around risk factors and protective factors. When asked what single intervention matters most, her answer was immediate: “The most important thing that we have to do is prevention. The fence. And the most important defence should start with parents.”
She referenced research published in 2019 showing that if parents use substances, their offspring are three times more likely to use. But here’s what’s fascinating: the specific message parents send matters enormously.
If a parent says, “I don’t want you to use cannabis,” children typically won’t use cannabis or other drugs. However, if a parent only says, “I don’t want you to smoke cigarettes,” the child may avoid cigarettes but will still use cannabis. Cannabis appears to be a barrier in a child’s mind. Get them to refuse cannabis, and they’re far more likely to refuse everything else.
This isn’t about perfection. It’s about presence. Dr Madras described how she became passionate about addiction neuroscience after realising at age 16 that substance use disorders are the only brain diseases we can prevent 100%, stop, intervene in, and treat.
“If the family is strong, the protective factors could surmount a lot of the difficulties and demons that people sense,” she explained.
Over 100 risk factors promote substance use. But strong families, genuine connection, love, structure, discipline, coaching, and nurturing create protective factors that outweigh those risks. When children feel genuinely connected and valued, substances don’t figure into their lives except as something to avoid.
The Meaninglessness Problem
Dr Madras offered a controversial but compelling theory about why substance use has become so prevalent in wealthy societies. She suggested that comfort and ease have created leisure time and boredom, removing the stressors that historically forced people to work hard and develop meaningful goals.
“People say poverty drives drug use. It does not,” she stated. “In so many areas of the world, poor people who work extremely hard every day don’t resort to drugs because they have to be competent to feed their families and survive.”
Western societies have removed almost all survival stressors. Some people believe drugs present the safest, quickest, cheapest way to feel good about themselves rather than having to strive like their ancestors did.
This ties into what researchers identify as “residing absurdity,” a deep sense of meaninglessness and purposelessness. The term “getting high” reveals what people are searching for: transcendence, something higher and more important than themselves. Drugs offer a shortcut to that transcendent feeling, a confidence trick played on the mind. Effective brain defence against drugs requires addressing this underlying search for meaning and purpose.
But the shortcut leads nowhere. It destroys the very brain that’s seeking meaning, systematically dismantling the capacity for genuine connection, achievement, and purpose.
Policy Battles and Bad Actors
Dr Madras recently secured a significant victory in reversing the 2018 farm bill that allowed hemp to be exploited as a loophole for legal intoxicating drugs. The bill permitted hemp to be grown with no more than 0.3% THC, but modern chemistry allowed companies to isolate and concentrate that THC, creating derivatives and analogues sold legally at petrol stations and cigar shops.
“It was a de facto legalised marijuana at the federal level,” she explained. Young people could buy these products with no restrictions because they were classified as hemp extracts. Even worse, some farmers would plant vast fields of what appeared to be hemp whilst growing cannabis inside them, knowing inspectors would simply drive past.
The pushback against reversing this loophole has been ferocious, including from Senator Rand Paul, whose libertarian ideology appears to have overwhelmed his medical training. But Dr Madras believes the reversal will hold.
This battle exemplifies the larger war for drugs, where bad actors use legal mechanisms, lobbying, and cultural narratives to normalise and commercialise substances that destroy young brains. Effective brain defence against drugs requires vigilance not just in homes and schools, but in policy arenas where commercial interests actively work to undermine protection. They insert language into bills via USB sticks handed to staffers. They fund research designed to muddy the waters on causation. They frame opposition as outdated moralism rather than scientific fact.
Building Fences, Not Just Ambulances
The metaphor of the fence at the top of the cliff versus the ambulance at the bottom perfectly captures the choice society faces. We can invest in treatment services, harm reduction programmes, and emergency interventions. Those have their place.
But Dr Madras’s answer was unequivocal: “The most important thing that we have to do is prevention. The fence.”
That fence must be built primarily by families. Parents who clearly communicate that substance use is unacceptable, who model healthy behaviour, who provide structure and genuine connection, dramatically reduce the likelihood their children will use drugs.
Schools, communities, and policies all play supporting roles. But without strong families as the foundation, other interventions are fighting an uphill battle against biology, peer pressure, and the relentless marketing of intoxication.
Dr Madras’s research makes clear that this isn’t about scare tactics or moralising. It’s about biological reality. Substances kill brain cells, alter gene expression, cause inflammatory damage, and create arrested development. The younger someone starts, the worse the damage.
The only “disease” we can prevent 100% is being systematically ignored in favour of managing its consequences. True brain defence against drugs means stopping substances before they enter young bodies, not managing the wreckage afterwards. We’re parking ambulances at the bottom of the cliff whilst dismissing anyone who suggests building a fence at the top.
This represents a catastrophic failure of public health priorities, one that will echo through generations as young people lose cognitive capacity, develop schizophrenia, and remain trapped in adolescent development well into middle age.
The science is clear. The solution is clear. The question is whether we’ll act on it.
Listen to the full conversation with Dr Bertha Madras on the Unnecessary Harm Podcast: A War in the Defense of Our Brains
Essential Resources:
Social Determinants & Substance Use – Beyond the Policy ‘Silo’ Pragmatics
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