Illicit cannabis use can result in a range of adverse physical and mental health outcomes. Long-term use of cannabis can result in impairments to cognitive functioning, including memory and attention. In general, more prologued use results in greater impairment – people who use cannabis for many years may not recover full cognitive function even when they stop using.

Inhaling cannabis smoke can also lead to respiratory problems such as bronchitis, airway injury and lung inflammation, and may increase risk of lung, throat, and oral cancer. In pregnant women, cannabis use is associated with impaired fetal development and reduced birth weight.

There is a strong association between cannabis use and psychosis or psychotic disorders such as schizophrenia. Among people with a genetic predisposition, cannabis use may trigger psychosis or make existing symptoms worse. Other mental health conditions are also associated with cannabis use, including depression and suicidal thoughts and behaviours.