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Medical Cannabis

Topic Overview

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​What is medical cannabis?

Cannabis (marijuana) is a dru​g that is made up of the leaves, flowers, and buds of the cannabis plant. Medical cannabis is cannabis prescribed for medical conditions such as cancer, AIDS, spasticity or multiple sclerosis. Medical cannabis can help treat symptoms like pain, nausea, and lack of appetite.

THC and CBD are the two main cannabinoids in the cannabis plant that are studied, though there are more than 100. THC affects how you think, act, and feel. It can make you feel "high." CBD can help you feel relaxed without the "high." And it may lessen pain and other symptoms.

There are many types, or strains, of cannabis. Each strain has a different THC-to-CBD ratio. Because of this, some strains have different effects than others. For example, if a strain of cannabis has a higher ratio of THC to CBD, it's more likely to affect your judgment, coordination, and decision making. 

What is it used for?

Medical cannabis may be helpful for some health conditions. These may include:​

  • Nausea and vomiting from chemotherapy (chemo) for cancer.
  • Low appetite and weight loss for people who have AIDS.
  • Muscle stiffness for some multiple sclerosis or spinal cord injury patients.
  • Chronic nerve pain or pain at the end of life.

Cannabis is available as a dried plant, oil extract, and products you put on your skin. It can also be added to homemade foods such as baked goods or candy (edibles). They usually contain both THC and CBD. Medicine that contains THC are also available. These include:

  • THC and CBD (Sativex). This is a combination medicine that can relieve pain in people with advanced cancer and relieve muscle stiffness in people with multiple sclerosis. This drug has naturally occurring THC.
  • Nabilone​ (Cesamet). This medicine ​is used to relieve nausea and vomiting caused by chemo. It may also improve the appetite of people who have AIDS. Nabilone contains man-made THC.

If you think you might want to try medical cannabis, talk to your doctor about what type of cannabis might help relieve your symptoms. You can also visit the Medical Use of Cannabis - Health Canada​ website for more information.

How is it used?

There are many ways people can use medical cannabis. More research is needed to understand the effectiveness of each of these different uses. 

For example, people can:

  • Smoke it as a dried plant.
  • Brew it into tea.
  • Inhale it as a vapour ( also called vaping).
  • Spray it under the tongue.​
  • Apply it to the skin.
  • Eat it in homemade foods (edibles).

How soon and how long you may feel the effects of cannabis depends on several things, including how it was taken. For example, when cannabis is smoked, the effects can usually be felt within seconds after inhaling. On the other hand, when cannabis is eaten, it may take several hours to feel the full effect. Since the effects aren't felt right away, people may think they need more and use too much. To avoid this, start with small amounts until you know how edibles affect you. Or follow your doctor's instructions on how much to use.

The type of cannabis you have used, how much you've used and how long you've been taking it can also affect how your body responds to it. You may feel the effects of cannabis for hours after you use it.

What are the risks of medical cannabis?

Cannabis can interact with many other medicines. It can be dangerous if you use it with medicines that make you sleepy or control your mood. These include sedatives, anxiety ​drugs, antidepressants, and opioids. It can also be dangerous to use cannabis with alcohol, tobacco, and/or other drugs.​

Cannabis can affect your blood pressure, so use caution if you take medicine for this condition. It also increases the chance of bleeding if you're on blood thinners.

Before you try cannabis, talk to your healthcare provider about other medicines you use. Also talk to your healthcare provider about any personal or family history of substance use disorder or mental health disorders. Using cannabis may make these problems worse.

Cannabis may affect your judgment, memory, concentration, coordination, and decision making. Don't drive or operate machinery after using cannabis.

Cannabis can affect different people in different ways. Side effects may include:

  • Dry mouth.
  • Red eyes.
  • Anxiety or paranoid thoughts.
  • Faster heart rate.
  • Dizziness.
  • Drowsiness.
  • Nausea and vomiting.

Long-term regular use of cannabis may increase your 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.

If you smoke cannabis, the smoke can make you cough and wheeze. It can even damage and irritate your lungs and airways. This can lead to bronchitis (an irritation of the airways that lead to your lungs).

If you are using medical cannabis and are pregnant or think you might be or are breastfeeding, talk to your healthcare provider. It can affect your baby's development.

Can regular use lead to cannabis use disorder?

Some people who regularly use cannabis may develop cannabis use disorder​. This can range from mild to severe (dependency). They may find it hard to control their use and keep using cannabis even though it's having harmful effects on their lives.

The risk of cannabis use 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 disorders.

People who use cannabis often and then quit may have withdrawal symptoms. These include anxiety, trouble sleeping, and intense cravings for the drug.

How can you reduce the risk of harm from cannabis use?

Using cannabis isn't risk-free. But there are things you can do to reduce your risk of getting sick or injured.

Lower-risk use.

  • All forms of cannabis use have health risks. The only way to completely avoid these risks is by choosing not to use cannabis.
  • You will lower your risk of cannabis-related health problems if you choose to start using cannabis later in life. The earlier in life you begin using cannabis, the higher your risk of serious health problems.
  • Choose products that have low levels of THC or a higher ratio of CBD to THC. Read the label of any products you're thinking about trying. The type or strain, strength, and effects of cannabis can vary greatly.
  • Don't use synthetic cannabis, such as K2 and Spice. These drugs are stronger than cannabis and can have very bad side effects. While cannabis is in the name, these synthetic drugs do not come from the cannabis plant.
  • Avoid smoking cannabis. The smoke can damage your lungs. Other forms of cannabis use, such as vaping or edibles, are better for your lungs but still have health risks.
  • If you choose to smoke cannabis, avoid breathing​ in deeply or holding your breath.
  • Try to limit your cannabis use to 1 day a week, at most.
  • Don't drive or operate machinery after using cannabis. Using cannabis may affect your judgment, coordination, and decision making. It can also increase your risk of being in a car crash. Make a plan to get home safely. For example, choose a designated driver or take a taxi or bus for a safe ride home.
  • Avoid cannabis if you have a personal or family history of psychosis or substance use problem. Pregnant women should not use cannabis at all.
  • ​Avoid combining any of the risky behaviors described above.

Know what you're using.

  • Understand how soon you may feel the effects of the product you use, and how long those effects may last. Ask your healthcare provider what you can expect. The product label may also have this information.

Keep others safe.

  • Store cannabis in a safe and secure place. This is especially 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 them.
  • Protect others from second-hand smoke. It is unsafe to smoke with children and others present. Second-hand cannabis smoke can cause babies and young children to be sick and it can affect their levels of alertness, understanding, and judgement. If you're around someone who is smoking cannabis, you may feel some effects of the drug.

Know when to call for help.​

Contact your healthcare provider if you have unwanted side effects or you think you have a problem with cannabis use.​

Current as of: April 9, 2019

Author: Adapted with permission of Healthwise ®