Cannabis Made Clear

The Effects of Cannabis on the Brain

While cannabis can be consumed in a responsible way, there are still inherent risks with regular use — including to the brain. Here are some of the short- and long-term effects regular cannabis use can have on the human brain.

Cannabis and the Brain

For many people, cannabis can be consumed in a way that reduces the risks. But that doesn’t mean cannabis is a harmless substance. Like all regulated psychoactive substances (including alcohol and tobacco), cannabis has the potential to cause harm. Regular consumption (defined as weekly or more frequent cannabis use over a period of months to years) comes with potential health risks to our bodies, including our brains.

Everyone reacts differently to cannabis. Regardless of the consumption method, regular cannabis use can have negative cognitive (brain function) health outcomes for some individuals. Understanding the risks can help you make informed decisions about consuming cannabis.

Potential short-term cognitive effects

Below are some of the potential short-term effects of cannabis on the brain, caused by impairment. While these effects are most often temporary, some can be uncomfortable, overwhelming or even dangerous, depending on the place and situation.

Changes in perception Some individuals may experience time distortion and changes in their perception.
Sleepiness (fatigue) Depending on the dosage, as well as a consumer’s individual factors, THC and CBD can induce sleepiness.
Impaired ability to remember, concentrate, pay attention Impairment of short-term memory and ability to concentrate is a common effect.
Feelings of anxiety, panic; psychotic symptoms Some individuals, and most commonly inexperienced individuals, may experience anxiety, panic and psychotic symptoms. Potent doses of THC can induce feelings of paranoia, delusions and dissociation.
Feelings of joy and calm Some individuals may experience feelings of euphoria and relaxation.
Reduced ability to react quickly Whether you’re driving a car (or other motor vehicle), riding a bike or operating machinery, cannabis use increases your risk of causing injury to yourself (and others). Depending on the potency, dose, consumption method and individual factors, impairment can last 24 hours.

Potential long-term cognitive effects

For some individuals, regular cannabis use also presents the risk of long-term brain effects and conditions.

Impaired ability to remember, concentrate, pay attention Regular cannabis use is associated with mild cognitive impairment (such as difficulties in learning, making decisions and memory recall), which are often resolved with periods of abstinence. When regular use begins in adolescence and continues through young adulthood, cognitive impairment may be greater and long-term. Research suggests that cognitive deficits may be diminished with abstinence.
Cannabis use disorder An estimated one in three people who consume cannabis will develop a problem with their use; 9% of people will develop a cannabis use disorder. This number rises to 17% for those who started consuming cannabis in adolescence. The risk of addiction is between 25% and 50% for those who consume cannabis daily. (For comparison, the CAMH 2014 Cannabis Policy Framework reported the probability of developing a dependence is about 68% for nicotine, 23% for alcohol and 21% for cocaine.) Learn more about cannabis use disorder and its risk factors.
Psychosis; schizophrenia Regular cannabis use can increase the risk of developing schizophrenia and/or experiencing psychosis; those with a family history of psychosis and/or schizophrenia are at the greatest risk. For individuals without a family history, regular cannabis use is still a risk factor for these disorders, especially with frequent use and consumption of products high in THC, and if consumption began in adolescence. Learn more about cannabis and mental health.

Effects on the developing brain

Even though Canadian adolescents are legally considered adults by age 18 or 19 (depending on their province or territory), the human brain continues to develop until around the age of 25. The developing prefrontal cortex, which is the centre of decision-making, problem-solving, memory and emotional regulation, is especially vulnerable to cannabis compounds. The potential connections between negative impacts to the brain and regular cannabis use that begins in adolescence are being uncovered but are not yet fully understood.

Learn more about cannabis and the developing brain.

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Clearing the Smoke on Cannabis: Regular Use and Mental Health
Canadian Centre on Substance Use and Addiction

Substance Abuse in Canada: The Effects of Cannabis Use During Adolescence
Canadian Centre on Substance Use and Addiction

Health Effects of Cannabis
Government of Canada

Association of Cannabis With Cognitive Functioning in Adolescents and Young Adults: A Systematic Review and Meta-analysis
JAMA Psychiatry

Addiction to Cannabis
Government of Canada

Cannabis Policy Framework
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