Cannabis has a long history as a medicine and was a part of medical practice until the late 19th century. The discovery of cannabidiol (CBD) and 9-tetrahydrocannabinol (THC) in the mid 20th century, and then the various components of the endocannabinoid system (ECS) over the following decades has again brought cannabis back into the public eye as a potential therapeutic agent. At present, cannabis is being used in the community across the world for both recreational and medical purposes. In the case of medical usage, it may be prescribed by a medical doctor or purchased either legally or illicitly for medical purposes such as symptom relief. Evidence for cannabis as a medicine is still an emerging field, and while potential mechanisms of action for a variety of conditions have been elucidated, including cancer, epilepsy and chronic pain, high quality randomized controlled trials in humans are still lacking. Despite popular beliefs, cannabis, like all other medicines, has potential benefits and harms, and long-term consumption of cannabis, even for medical reasons, may not be risk free. In addition, consumption via modes of administration such as smoking or using a bong may increase the risk of negative health outcomes.