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Medical Cannabis: Modes of Use and Side Effects

Olga Kagan, Director of Permit Issuance, Medical Cannabis Unit
15 June 2025

Medical cannabis can be used in different ways, for example:

  • Smoking
  • Vaporizing
  • Ingesting

Every patient must go through training from a doctor who is qualified to do so before beginning medical cannabis therapy. When deciding on a therapy, the doctor will tell the patient of the possible ways of use and then customize one of them to fit the patient's needs, including figuring out the right dose. The doctor's instructions will be repeated by the pharmacist who dispenses the medical cannabis.

Note

Note

Medical cannabis can have side effects. The doctors and pharmacists will talk to you about the possible side effects and how to spot and handle them.

Possible side effects of medical cannabis

  • Side effects that increase the risk of falling and accidents: dizziness and poor balance, drop in blood pressure, drop in sugar levels, poor awareness and coordination.
  • Physical side effects: constant nausea and vomiting, seizures.
  • Mental health side effects: anxiety attacks and psychosis.
  • Pregnant women: impaired fetal development; developmental and behavioral disorders in children who were exposed to cannabis in the womb.
  • Cognitive side effects: impairment of short-term memory, changes in temporal and spatial perception, and attention difficulties.
  • Overdose: confusion, drowsiness, dizziness, constant vomiting, and seizures. In children, an overdose may cause respiratory depression.
  • Psychosis: anyone who has a history or genetic predisposition, cannabis may cause hallucinations, trigger psychotic attacks, and anxiety.
  • In prolonged use: side effects may also include development of a dependence (addiction) and smoking-related damage, for those who smoke cannabis.
  • Older adults: higher risk of falling and memory problems, dangerous interaction with other medicines. Older adults should be trained with the help of another adult, and they should learn how to avoid falls and hypoglycemia, which is a severe drop in blood sugar.

Advice on how to deal with side effects

  • In the first few times you use medical cannabis

    It is recommended to start using medical cannabis at home, where you can relax, and with another adult nearby. You should have a lot of candy or a sweet drink on hand.

  • Self-consumption log

    Every time you use medical cannabis, you should write down in a log how it affects your symptoms and note any unwanted effects. This log will help your doctor understand how successful the therapy is and make changes as needed.

    More information about the log and the available download

For Your Information

For Your Information

Medical cannabis use is a new area that is still growing. As new ideas are brought to the table, they need to be carefully considered. This is particularly important because there is evidence that medical cannabis therapy can help, but there is also evidence that it can cause damage. As an example, there is proof that cannabis can help people with PTSD sleep better, have fewer flashbacks, and get back to normal sleep-wake cycles after hyperarousal. But different sources say different things about the long-term effects of cannabis use. Some studies show that people with post-traumatic stress disorder have more serious symptoms, such as being addicted to cannabis and not being able to complete daily functions.

If you think you are having side effects that are bothering you, you should talk to your doctor or pharmacist. It is important that you tell the doctor who gave you medical cannabis about the side effects you experience.