The Criminal Code prohibits people from driving while impaired by alcohol, drugs, or both. While cannabis is legal in Canada, you can still be charged with impaired driving if you have between two and five nanograms (or higher) of THC per ml of blood in your system. When alcohol and cannabis have been taken in combination, the prohibited level is 50mg or more of alcohol per 100ml of blood and 2.5 nanograms or more of THC per ml of blood.