Possible interactions include:

Alcohol. Cannabis might make the effects of alcohol more obvious. This may include changes in mood and reaction time.
Anticoagulant or antiplatelet medicines, herbs and supplements. These types of medicines, herbs and supplements may make you bleed more if you have a cut or injury. Using these with cannabis might raise the risk of bleeding, especially for those taking warfarin (Jantoven).
CNS depressants. Using cannabis with medicines that lower the activity of the brain and spinal cord, called the central nervous system, might make a person sleepier and slower to respond.
Protease inhibitors. Using cannabis may make these medicines not work as well.
Medicines to prevent seizures. Avoid using cannabis when taking medicines to treat seizures. The medicines may not work as well or cause other side effects, such as liver conditions.

Avoid using cannabis until you review your medicines with a healthcare professional or pharmacist.