Health risks of marijuana use

Evidence clearly shows that using marijuana has health risks. As marijuana containing higher levels of tetrahydrocannabinol (THC) is becoming more commonplace, the use of this stronger type of marijuana can contribute to increased health risks. In fact, today's marijuana is stronger than marijuana from many years ago. Studies show that the average level of THC, the principal "mind-altering" component of marijuana, has increased by 300% to 400% over the last few decades.

Marijuana is the most widely used illegal drug among youth today. Starting to use marijuana young can greatly increase physical and mental health risks. It also increases the chance of addiction.

Youth are especially vulnerable to the health effects of marijuana use because adolescence is a critical time for brain development. Having THC in the brain at such a critical time can therefore interfere with brain development and harm brain function. It can also increase the risk of triggering a psychotic episode or a mental illness such as schizophrenia.

Learn about the mental and physical risks to one's health from regular marijuana use.

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Physical effects of marijuana abuse

Short-term effects

Physical effects of short-term (acute) marijuana use can include:

  • red eyes,
  • increased heart rate,
  • drop in blood pressure,
  • light-headedness (fainting),
  • heart attack, and
  • stroke.

Long-term effects

The physical health effects of marijuana use mainly involve your lungs and heart.

Lung and breathing problems

Like tobacco smoke, marijuana smoke is a mix of toxic substances. Marijuana smoke irritates the throat and lungs, causes coughing, and is associated with symptoms of bronchitis. Marijuana smoke also contains many of the same cancer-causing materials as tobacco smoke.

Regular marijuana smokers may suffer the same symptoms as tobacco smokers, such as:

  • chronic (ongoing) cough,
  • increased phlegm buildup in the throat (mucus),
  • frequent chest problems, and
  • greater risk of lung infections.

Heart problems

The heart normally beats about 70 to 80 times a minute, but using marijuana can double that rate. This increased rate can put a lot of stress on the heart. Smoking marijuana can also cause an increased risk of stroke. The risks of heart attack or stroke from marijuana use appear to increase with age and with pre-existing heart or blood circulation problems.

Pregnancy problems

Women who are pregnant may be particularly at risk for health problems related to marijuana use.

Marijuana smoking during pregnancy has been associated with long-lasting harm to the exposed child's memory and other brain functions as well as hyperactive behaviour. Like alcohol, the toxins in marijuana are carried in the mother's blood to her unborn child. Marijuana use mainly affects the development of the fetus' nerves and brain.

The toxins in marijuana are also carried in breast milk and can be passed to her growing baby.

Studies show that some babies born to women who used marijuana during pregnancy tend to have:

  • delayed visual responses,
  • shaking,
  • a high-pitched cry, and
  • decreased birth weight.

In older children, problems are often seen while they are at school. Exposure to marijuana may affect their:

  • memory,
  • problem-solving skills,
  • emotional and behavioural responses, and
  • ability to maintain focus and pay attention.

Did you know?

Studies show that the average level of THC, the principal "mind-altering" component of marijuana, has increased by 300% to 400% over the last few decades. Learn more about marijuana.

Mental effects of marijuana abuse

Short-term effects

Mental effects of short-term (acute) marijuana use can include:

  • loss of short-term memory,
  • impaired ability to focus and pay attention,
  • impaired ability to concentrate and learn,
  • loss of motor coordination,
  • poor reaction time,
  • impaired judgement and ability to think,
  • sleepiness,
  • dizziness,
  • fatigue,
  • psychotic episodes,
  • mild paranoia, anxiety, and fear,
  • panic attacks,
  • perceptual distortions (visual, auditory),
  • severe agitation,
  • disorientation, and
  • confusion.

Long-term effects

THC is the substance that is responsible for most of the effects of marijuana. THC levels in marijuana today are much higher than they have been in the past. Some of the harmful effects of marijuana can last for hours, days, weeks, months and even years after last use. Regular long-term marijuana use can:

  • harm concentration,
  • cause loss of memory,
  • harm the ability to think and make decisions, and
  • decrease IQ.

The risks of experiencing these harmful effects increase in those who start using marijuana regularly as a teenager. Youth are especially vulnerable to the health effects of marijuana use, including harmful effects on mental functioning, and psychosis and schizophrenia.

Some people who use marijuana may be at higher risk of developing mental illnesses like psychosis or schizophrenia, including those who:

  • have a personal or family history of psychosis and/or schizophrenia,
  • start using marijuana young,
  • use marijuana daily or a few times a week, and
  • use marijuana for months or years.

Even if a marijuana user does not develop a mental disorder, the drug's effects can ruin school and work performance.

Marijuana addiction

Marijuana addiction can have a number of harmful consequences on health, but it can also harm one's social, scholastic, professional and financial future.

Marijuana use that begins early and continues over time can lead to changes in the brain and body that contribute to developing an addiction to marijuana. Once an addiction has developed it may be very hard to stop using marijuana, even though it interferes with daily life.

Marijuana use that begins early in adolescence, that is frequent and that continues over time can lead to addiction. It is estimated that 1 in 9 marijuana users will develop an addiction to marijuana.

This number rises to about 17% for people who started using marijuana as a teenager. If a user smokes marijuana daily, the risk goes up to between 25-50%.

Get help

Are you struggling with drug abuse? Is someone you care about having a problem?

Help is available, whether you need it for yourself, a friend, or a family member.

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