Cannabis and your heart health

Cannabis, or marijuana, is a plant that is used to produce different effects on the body and the mind. It can be used in many forms, such as:

• Dried flowers, leaves or buds (often smoked or vaped)
• Hash or cannabis extracts (such as oils and shatter)
• Edible products (such as candies, cookies, or butter)

Cannabis may be prescribed by a doctor to help manage certain medical conditions, but most people use it without a prescription, often for recreational purposes.

Cannabis contains many compounds, including more than 100 active compounds, called cannabinoids. The two most well-known cannabinoids are:

• THC (delta-9-tetrahydrocannabinol): This is the main psychoactive ingredient that causes the “high” feeling with cannabis use.
• CBD (cannabidiol): This has little to no intoxicating effect and doesn’t make you feel high.

Different cannabis products can contain different amounts of THC and CBD. These amounts are usually listed on the label (in milligrams or as a percentage).

Most of the heart-related effects are linked to THC, the main psychoactive component of cannabis; however, CBD can also affect your health.

While many people view cannabis as natural or harmless, it is important to know how it may affect your heart and blood vessels, especially if you already have heart disease or concerns.

• Increases heart rate: Using cannabis can cause your heart rate to increase. In some people, this may increase the chance of having irregular heartbeats.
• Changes blood pressure: Cannabis can cause your blood pressure to drop shortly after using it, which may make you feel dizzy or lightheaded. Later, your blood pressure may rise, which can add extra strain on your heart and blood vessels.
• Makes the heart work harder: Cannabis can make your heart work harder than usual. If you already have heart problems, this extra effort may increase your chance of chest pain (angina), heart attack, or heart failure.
• Higher risk of stroke: Some studies have shown that people who use cannabis may have a higher risk of stroke. Daily cannabis use increases your risk of stroke by up to 42% compared to people who do not use cannabis.
• Interactions with medication: Both THC and CBD interact with a variety of medications, changing how they work in your body. For example, CBD can increase the risk of bleeding if you are on blood thinners.
• Contributes to breathing problems: Smoking cannabis adds chemicals like tar and carbon monoxide in your lungs. This can lead to symptoms like coughing, wheezing, and/or chronic bronchitis. Breathing in smoke, whether from smoking cannabis or tobacco, also reduces the amount of oxygen your heart gets.

These effects can happen regardless of how you use cannabis (smoking, vaping, edibles, oils, etc.), although inhaling cannabis smoke or vapour carries higher risks.

• Anesthesia: Cannabis can make it hard to predict the amount of medication needed to keep you comfortable during and after surgery.
• Pain and nausea: Cannabis can make it harder to control your pain, and you may have worse nausea after surgery.
• Breathing problems: Smoking can lead to breathing problems during surgery.
• Cardiac effects: Cannabis can increase or decrease heart rate and blood pressure during surgery.
• Medications: Cannabis might interact with other medications.
• Wound healing: Smoking cannabis can lower the oxygen in your blood meaning you may take longer to heal.
• Withdrawal after surgery: Cutting back your cannabis use before surgery lowers your risk of cannabis withdrawal after surgery.

Due to the effects of cannabis on your surgery, reduce your cannabis use as early as possible and stop using cannabis at least 72 hours before surgery.

Download "Cannabis and your upcoming heart surgery" (PDF)

You may face higher risks to your heart while using cannabis if:

• You have heart disease: If you have heart disease, using any amount of cannabis can make it worse and increase your risk of heart attack, stroke, or chest pain.
• You use cannabis daily or often: More frequent cannabis use is associated with higher risks of heart problems.
• You smoke cannabis: Inhaling cannabis smoke (such as from joints or water pipes) adds stress to your lungs and heart and lowers the amount of oxygen your heart receives. The risk of a heart attack is higher in the first hour after smoking cannabis.
• You have high blood pressure: Cannabis can make high blood pressure worse, which increases the strain on your heart and blood vessels, which can lead to heart disease and stroke. 

There are no 100% risk-free cannabis products or methods of use. Not using cannabis is still the best way to avoid health risks. But if you choose to use cannabis, there are things you can do to reduce harm and support your heart health.

Ways to reduce risk:

• Avoid smoking or vaping cannabis. Try edibles, oils, or capsules instead.
• If eating cannabis products, start low and go slow. Edibles can take longer for you to feel the effects, and it’s easy to take too much. Always read the label and wait before using more.
• Choose products with low THC, or a higher CBD content. CBD content does not eliminate the harm from THC and should also be used with caution.
• Avoid daily cannabis use. Try alternating days or cutting back to once a week.
• Buy cannabis products from a licensed retailer to ensure product quality, reduce the risk of contamination, and have more reliable information on product ingredients.
• Avoid synthetic cannabis products, like K2 or spice.

• If you are using cannabis, it’s a good idea to speak with a healthcare provider about your use. They can help you understand how cannabis might affect your health or interact with your medications.
• If you’re waiting for cardiac surgery, cannabis use can affect anesthesia, wound healing and pain management. Discuss your cannabis use with your surgical team. More information is available in the Cannabis and your upcoming heart surgery handout.
• It would also be a good idea to speak with your medical team if you are finding it hard to cut back, or if cannabis is getting in the way of important things in your life. 

• University of Ottawa Heart Institute: Cannabis and your upcoming heart surgery (PDF)
• Public Health Agency of Canada: Canada’s Lower-Risk Cannabis Use Guidelines
• Ottawa Public Health: More information on cannabis, services and resources.
• AccessMHA: Coordinated access and navigation to free mental health, substance use services in Eastern Ontario.
• Connex Ontario: Information on mental health and addiction treatment services across Ontario. 1-866-531-2600.

Download this page:

Cannabis and your heart health (PDF)