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What is cannabis?

Cannabis (marijuana) is a drug that's made up of the leaves, flowers, and buds of the cannabis plant. People may use cannabis for medical or recreational reasons. The two most active chemicals in cannabis are THC and CBD. THC can make you feel "high." CBD can help you feel relaxed without the "high."

How is it used?

There are many ways people can use cannabis. For instance, people can smoke it as a dried plant or inhale it as a vapour. They can brew it into tea, spray it under the tongue, or apply it to the skin. Or they can eat it in prepared or homemade foods (edibles).

What are the short-term effects of cannabis use?

People often use cannabis for the way it makes them feel. Or they may use it for medical reasons. Using it may make them:

  • Feel relaxed or very happy ("high").
  • Have less chronic pain or nerve (neuropathic) pain.
  • Feel hungry so they eat more.

Cannabis can also cause unwanted side effects, such as:

  • Impaired short-term memory and ability to concentrate.
  • Poor judgment and coordination.
  • Feeling anxious.
  • Paranoid thoughts.
  • Faster heart rate.
  • Red eyes and dry mouth.
  • Feeling dizzy.
  • Nausea and vomiting.
  • Changes in blood pressure.

What are the risks?

Long-term use of cannabis may increase the risk of problems such as:

  • Trouble with learning, memory, and concentration. This is most likely if regular heavy use starts in the teen years.
  • Lung problems if you smoke cannabis. This can lead to coughing or wheezing and lung infections like bronchitis.
  • Mental health problems like anxiety, depression, and psychosis. This is more likely if you have a personal or family history of these disorders or use cannabis products that have high levels of THC.
  • Cannabis use disorder. Some people who use cannabis may find it hard to control their use. They may keep using cannabis even though it's having harmful effects on their lives. The disorder can range from mild to severe. People who use cannabis often and then quit may have withdrawal symptoms. These symptoms include anxiety, trouble sleeping, and intense cravings for the drug. The risk of this disorder is higher in people who:
    • Start using cannabis when they're young.
    • Use it every day.
    • Have other substance use disorders and mental health problems.
  • Increased risk for severe nausea and vomiting (cannabinoid hyperemesis syndrome, or CHS). People who have CHS may feel very thirsty and have belly pain and diarrhea. They may vomit more than 20 times a day. Bouts of vomiting may last more than 24 hours.

How does using cannabis while you're pregnant affect your baby?

Using cannabis isn't safe for you or your baby. If used during pregnancy, it can harm a developing baby (fetus). It can pass from the mother's blood to the baby's blood. And it can pass from your breast milk to your baby during breastfeeding.

Cannabis can cause problems for you during your pregnancy and when it's time for your baby to be born. It may also affect your baby both before and after the birth. This is even more true for people who regularly use a lot of cannabis.

Health Canada says that cannabis use during pregnancy may:footnote 1

  • Cause your baby to be smaller at birth.
  • Be linked to problems with brain development, learning, and behaviour.
  • Increase your baby's risk for depression or anxiety later in life.

THC is found in breast milk. It can cause problems with feeding. Health Canada says that babies exposed to THC in breast milk may:footnote 1

  • Be drowsy.
  • Have muscle weakness, which can make it hard for your baby to hold their head up.
  • Not suckle well.

How are young people affected by using cannabis?

Using cannabis before the age of 25 can affect a young person's brain development, as well as emotional and social development. Some young people who use cannabis may develop cannabis use disorder. They may find it hard to control their use. They may keep using cannabis even though it's having harmful effects on their lives.

Cannabis affects the parts of the brain that deal with judgment, decision making, and emotions. This can make it harder for young people to think, learn, reason, remember, solve problems, and make good choices. And they may be less able to control their emotions and actions. For example, they may engage in risky behaviours like driving when "high," having unsafe sex, binge drinking, or using other drugs.

Young people who use cannabis may be more likely to have anxiety and depression than others who don't. And they may have more problems in school, relationships, and work.

What can you do to lower your risk when using cannabis?

  • To have the lowest risk, don't use cannabis. But if you do use it, limit your use to 1 day a week at most. footnote 2
  • Know what you're using. Choose products that have low levels of THC. The type (or strain), strength, and effects of cannabis can vary greatly. And understand how soon you may feel the effects of the product you use and how long those effects may last. The product label may have this information.
  • Don't drive or operate machinery after using cannabis. Using cannabis may affect your judgment, coordination, and decision making.
  • Don't smoke cannabis. The smoke can damage your lungs. If you do smoke it, don't breathe in deeply and don't hold your breath. footnote 2
  • Don't use cannabis with alcohol, tobacco, or illegal drugs.
  • Reduce the risk of medicine interactions. Cannabis can be dangerous if you take it with blood thinners or with medicines that make you sleepy, control your mood, or lower your blood pressure. Talk to your doctor about other medicines you use before you try cannabis.
  • Keep others safe. Store cannabis in a safe and secure place. This is even more important with edible cannabis, which can be easily mistaken for treats or snacks. Make sure that children, friends, family, and pets can't get to it. And protect others from second-hand smoke.

Synthetic cannabis

Synthetic cannabis is made of dried plant material that is treated with chemicals that produce effects like cannabis's effects. It is sold in the form of incense under many names, such as K2 or Spice. The labels often claim that these products are "safe" or "natural." But in fact, the active chemicals are created in a lab. And they have not been tested for safety.

Some people try these products because they are easy to buy and they may not be detected by drug tests.

People think that using these drugs will make them feel the same as when they use cannabis. But these drugs can be stronger than cannabis. And the effects are hard to predict. That's because the type and strength of the chemicals used are often unknown. Some people have reported severe symptoms, such as:

  • Fast heart rate and high blood pressure.
  • Vomiting.
  • Feeling agitated or confused.
  • Feeling like others want to harm them (paranoia), or seeing or hearing things that aren't there (hallucinations).



  1. Government of Canada (2018). Is cannabis safe during preconception, pregnancy, and breastfeeding?: Cannabis evidence brief. Government of Canada. Accessed February 27, 2019.
  2. Public Health Agency of Canada. (2019). Canada's lower-risk cannabis use guidelines. Government of Canada. Accessed April 26, 2022.


Current as of: March 21, 2023

Author: Healthwise Staff
Clinical Review Board
All Healthwise education is reviewed by a team that includes physicians, nurses, advanced practitioners, registered dieticians, and other healthcare professionals.

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