Safety and side effects

Medical cannabis, also called weed or marijuana, is generally considered safe. Most of the side effects of cannabis are due to the THC content. But different types of cannabis have different amounts of THC. This can make it very hard to know the right amount to take. The side effects seem to be worse the higher the dose of THC a person uses.

Cannabis can cause:

• Headaches.
• Dry mouth.
• Red and dry eyes.
• Dizziness and higher risk of falling.
• Drowsiness, including problems focusing.
• Fatigue.
• Coughing.
• Wheezing.

Other side effects may include:

• Nausea and vomiting.
• Feeling anxious.
• Seeing, hearing or smelling things that aren't there, known as hallucinations, and psychosis.
• Problems with memory.
• Heart that beats too fast.
• Heart that beats out of time.

Using doses of CBD higher than 300 milligrams a day can cause nausea, vomiting, diarrhea and liver conditions.

Cannabis affects how well you pay attention and move. It can affect your ability to think clearly. Don't drive or use machinery when using cannabis.

If you have a mental health condition, use cannabis with caution. If you have bipolar disorder, cannabis may make you irritable or restless with racing thoughts, also called mania. Using cannabis often might raise the risk of depression or make depression symptoms worse. Research in people who have schizophrenia suggests that cannabis use may raise the risk of losing touch with reality, also called psychosis.

Cannabis slows down messages to the brain and spinal cord, also called the central nervous system. This system is sometimes called the CNS. Using cannabis can change how you think and feel. Some people may have heart changes, such as high blood pressure. Using cannabis often for years may worsen lung conditions and may cause serious, frequent vomiting, also called cannabinoid hyperemesis syndrome.

Avoid using cannabis for two weeks before getting medicine that puts you in a sleeplike state before surgery. This medicine is called an anesthetic. Using cannabis may cause you to need more anesthetic. Using cannabis also may raise your risk of anesthesia complications, such as a very fast heart rate.