Cannabis for medical purposes: Side effects
On this page
- About side effects
- Side effects of cannabis
- Side effects during pregnancy and breastfeeding
- Medical emergencies
- Possible health concerns from long-term use
- If cannabis use becomes a problem
- Report side effects
About side effects
Side effects are unpleasant or unwanted effects that may occur when you take a drug, medication or vaccine.
Information on side effects from the medical use of cannabis is limited.
Side effects may be due to:
- using too much cannabis
- another ingredient in the cannabis product
- your own sensitivity to the effects of cannabinoids such as THC and CBD
- a pre-existing health condition or a health condition that’s getting worse
- an interaction between the cannabis and other medications or substances you use
If you use cannabis for medical purposes and you experience side effects, consult with your health care provider.
Learn more:
Stop using cannabis and seek immediate medical attention if any of your side effects are a significant concern to you.
If you have accidentally taken cannabis or have taken too much, call for advice:
- 1-844-POISON-X (1-844-764-7669) or
- 1-800-463-5060 in Quebec
Side effects of cannabis
The following lists are possible side effects that could occur when you use cannabis. These are not complete lists of all possible side effects. Discuss any side effects with your health care provider.
Some side effects from smoking or vaping cannabis are similar to smoking tobacco or vaping nicotine, such as:
- cough
- shortness of breath
- chest pain or discomfort
- throat and lung irritation
Examples of THC side effects include:
- seizures
- dry mouth
- hallucinations
- blurred vision
- fast heartbeat
- nausea, vomiting
- feeling “too high”
- reduced inhibition
- increased appetite
- feeling tired or sleepy
- red, irritated, or dry eyes
- dependence or addiction
- feeling disoriented or confused
- psychosis, which occurs when you:
- hallucinate
- don’t know what’s real
- have false beliefs or disorganized thoughts
- severe anxiety or severe low mood
- thinking of harming yourself or others
- local skin reactions (redness, rash, itch)
- feeling suspicious, anxious, panicked or paranoid
- thinking differently than usual or thinking abnormally
- severe allergic reaction that could include a combination of:
- hives
- fainting
- dizziness
- rapid heartbeat
- difficulty breathing
- swelling of the eyes, throat or tongue
- difficulty focusing, remembering, thinking or making decisions
- cannabinoid hyperemesis syndrome, which involves repeated episodes of:
- severe nausea
- intense and prolonged vomiting
- stomach pain that’s resistant to treatment
- loss of balance or coordination, dizziness, headache or feeling lightheaded or faint
Examples of CBD side effects include:
- fever
- cough
- weakness
- decreased appetite
- feeling tired or sleepy
- local skin reactions (redness, rash or itch)
- nausea, vomiting, diarrhea or constipation
- liver problems, which can cause symptoms such as:
- fatigue
- nausea
- vomiting
- loss of appetite
- abdominal pain
- unusual darkening of the urine
- yellowing of the skin or the whites of the eyes (jaundice)
- a severe allergic reaction that could include a combination of:
- hives
- fainting
- dizziness
- rapid heartbeat
- difficulty breathing
- swelling of the eyes, throat or tongue
Side effects associated with other cannabinoids such as CBN, CBG, CBC, and THCV aren’t well known.
Side effects during pregnancy and breastfeeding
Using cannabis during pregnancy can:
- harm your fetus (unborn baby)
- affect brain and behavioural development of children
Cannabinoids in cannabis are transferred from the mother to the child and can harm your baby.
Learn more:
Medical emergencies
If you experience a medical emergency related to cannabis, call 9-1-1 and tell the operator you used cannabis.
Here are some examples of medical emergencies:
- seizures
- chest pain
- trouble breathing
- loss of consciousness
- trouble understanding, reading or speaking
- abnormal or unusual thoughts such as thoughts of suicide
- serious allergic reactions resulting in rash, hives, itch or swelling (especially of face, tongue, and throat), severe dizziness, trouble breathing
Possible health concerns from long-term use
Smoking cannabis can:
- expose you to the same harmful and cancer-causing chemicals found in tobacco smoke
- increase your risk of a chronic cough or other lung problems, especially if you smoke regularly
Vaping dried cannabis and cannabis extracts can expose you to substances that may cause potential long-term lung damage.
More research is needed to better understand the impact of vaping cannabis products on lung health.
Some possible health effects that may occur from long-term use of cannabis include:
- liver problems
- problematic cannabis use
- decrease in the effects of cannabis (tolerance)
- changes in hormones that can affect the menstrual cycle and fertility
- withdrawal-type symptoms if you abruptly stop using cannabis, such as:
- chills
- anxiety
- craving
- irritability
- headache
- restlessness
- stomach pain
- depressed mood
- anger or aggression
- shakiness and sweating
- insomnia or sleep difficulties
- nightmares or strange dreams
- decreased appetite or weight loss
- cannabinoid hyperemesis syndrome, which involves repeated episodes of:
- severe nausea
- intense and prolonged vomiting
- stomach pain that’s resistant to treatment
- increased risk of triggering or worsening psychiatric or mood disorders including:
- anxiety
- psychosis
- depression
- schizophrenia
- bipolar disorder
- decreased sperm count and other changes in the sperm that can affect male fertility
There may be other health effects of frequent cannabis use that we don’t yet know about.
If cannabis use becomes a problem
You may have problems with cannabis use if you:
- use it even if it harms your health
- keep using it even though you want to stop
- increase the amount you use but don’t notice any increase in benefits
- miss commitments at home, work or school because of your cannabis use
If you or someone you know needs support for problems with cannabis use, contact your health care provider or your local addiction treatment centre.
Learn more:
Report side effects
You can also report your side effects to your health care practitioner, the product manufacturer, or directly to Health Canada.
For more information, refer to: