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How does drug use affect mental illness?

By: Britany Rufenach


We all get overwhelmed sometimes. In a room with deafening noise, blinding lights, people constantly bumping into you – you’re probably scoping out the exit to get a breather. But if this overwhelming stimulus instead comes from within you, you can’t simply run away from the problem. Often, people suffering from mental health concerns turn to other routes of escape, like drugs and alcohol. Unfortunately, these self-medication routes provide only fleeting relief from their thoughts and emotions.

This method of escape can also lead to another complication: half of all people with severe mental illness have substance abuse problems. Substance use commonly occurs alongside anxiety, panic disorder, post-traumatic stress disorder, depression, bipolar disorder, attention deficit/hyperactivity disorder, and schizophrenia. But even if substances can seemingly help temporarily escape from a mental health crisis, how do they affect the onset and long-term course of mental illness?

The Chicken or the Egg – can drug use cause mental illness?

What came first: the substance use or the mental health issue? Establishing the cause vs. effect direction between drug use and mental illness is challenging. Take the example of a teenager going through life stressors – social pressure, family issues, problems at school. Perhaps they start smoking weed to calm their nerves and try to get themselves back into a good headspace. Gradually, this becomes a habit and they rely on it to help them feel ‘normal’. Later in life, they’re diagnosed with depression. Did drug use during a developmentally important period lead to changes in their brain structure, causing the mental illness? Did they already show sub-clinical symptoms of depression, or lack proper diagnosis, and turn to cannabis as relief? Or perhaps there are underlying vulnerabilities that made them more susceptible to both drug use and depression.

”If you put my hand into the fire and ask me to answer [which came first], I would say it's probably a chicken and egg question at this time,” quipped Dr. Jibran Khokar, a professor at Western University who studies substance use and schizophrenia. Schizophrenia is a serious mental disorder which is characterized by psychotic symptoms like hallucinations, delusions, and disordered thinking. Patients may also experience negative symptoms, like difficulty showing emotion and social withdrawal.

Substance use can worsen the course of schizophrenia – causing earlier onset, higher rates of hospitalization, treatment non-compliance, and (especially with alcohol) higher rates of violence and suicide. Of course drugs can also have physical health effects, which is especially problematic with an already vulnerable population, often leading to premature disability and death.

We know that genetics contribute to the development of schizophrenia from large datasets and family studies. One theory, sometimes called the “two-hit” model, suggests that this genetic vulnerability alongside an environmental stressor (like drug use or trauma) leads to schizophrenia. Under this model, genetics and drugs work together, so to speak, to cause the disorder. Indeed, high rates of cannabis use are associated with increased risk of psychosis and earlier onset, with heavy users having a 4-fold higher risk of developing it.

Up to a staggering 90% of patients with schizophrenia are chronic cigarette smokers. Nicotine activates a protein (called nAchR) in the brain that is important for the release of neurotransmitters; it plays a role in the reward/motivation system of the brain and general cognition. nAchR is present at lower levels in people with schizophrenia, which may partially explain some attention and memory deficits patients experience. The self-medication hypothesis suggests that individuals with schizophrenia may consume nicotine at such a high rate to compensate for their nAchR deficit, by causing more activation of the ones they do have. This would suggest that drug use is caused by the disorder, much like a fever is a symptom of an infection. Although nicotine may temporarily help to cope with some symptoms of schizophrenia, it can exacerbate other problems in the long run.

A unifying theory which could weave together these different ideas is the shared vulnerability hypothesis. Here, genetics is the primary cause. Genetic susceptibility makes a person more likely to use drugs and to develop a mental disorder. Drug use can trigger the disorder, and later the difficult symptoms of the disorder make the person more inclined to continue to use drugs. The chicken and the egg, as Dr. Khokar had phrased it earlier. People with mental illness can become trapped in a vicious cycle between substance use and disorder symptoms – a cycle they are dragged into by their genetics.

What if a person is able to escape that cycle? Dr. Khokar presents some optimistic news: “What we do know for sure is that if you can get somebody with schizophrenia to remain abstinent from a substance – studies have been done with both cannabis and cigarette smoking - you actually see improvements in all symptoms.”

What about other drug-disorder combinations?

This shared vulnerability idea holds true for other mental illnesses as well. Brain imaging studies suggest that ADHD is associated with changes in brain circuits that are also associated with drug cravings. In other disorders, brain circuits involved in reward, decision making, impulse control and emotions may be dysregulated. As for other drug-disorder combinations, Dr. Khokar explains “it does vary between the substance and the illness. And at the individual level, each person [will have different experiences]. We often look at this at a population level, but when you zoom in to each drug or each illness then different patterns can emerge.”

A constant between all combinations of drugs and disorders is that when treating a mental illness that occurs alongside excessive substance use, treating both at the same time is absolutely critical. It’s difficult to escape that vicious cycle when either triggering agent keeps pulling you back in.

Of course, casual & occasional drug use is different from chronic dependence. We should be mindful that excessive drug use may leave one more vulnerable to mental illness, just as mental illness may leave one more vulnerable to substance dependence. Ultimately, there shouldn’t be any shame or blame for substance use disorders or mental illness - it’s an overwhelming world out there and the genetic lottery isn’t kind to everyone.



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