The link between the use of cannabis and mental health problems is an issue that receives a great deal of attention in the research and general media. Although severe illnesses such as schizophrenia have received a large portion of this attention, there is also debate about whether the use of cannabis can lead to more common psychiatric disorders such as depression and anxiety.
There have been a number of studies that have explored the link between cannabis use and mental health symptoms. Strong associations are often found but this is not the same as a causal link (i.e. one causes the other).
Does smoking cannabis cause schizophrenia?
Psychosis refers to a number of mental illnesses where people experience difficulty in telling what is real and what is not. Someone suffering from a psychosis might hear voices that are not really there (hallucinations), or believe things that are not true (delusions). Schizophrenia is a form of psychosis.
There have been reports of people experiencing these psychotic symptoms after smoking a lot of cannabis or more cannabis than they are used to. This is rare and the symptoms, although frightening at the time, usually go away if use of cannabis is stopped. Cannabis has been shown to make psychotic symptoms worse in those who already have a psychotic disorder such as schizophrenia.
Some research suggests that cannabis can cause schizophrenia. Multiple studies have found that, in particular, using cannabis during adolescence increases the likelihood of experiencing symptoms of schizophrenia in adulthood (Arseneault et al., 2002; Parakh & Basu, 2013). Evidence suggests that cannabis may somehow trigger schizophrenia in those who are already at risk of developing the disorder, though this connection is not conclusive. Cannabis exposure may be a component or contributing cause which interacts with other known (genetic, environmental) and unknown factors, culminating in schizophrenia (Sewell et al 2009, Power et al 2014, Parakh & Basu 2013; Bloomfield et al. 2013). More research is needed in this area.
Those with a vulnerability to develop schizophrenia, such as having a family history of the illness, should be strongly advised against using cannabis. People with existing psychotic disorders should be strongly advised and assisted to cut-down and/or cease their cannabis use.
Does smoking cannabis cause depression or anxiety?
The link between cannabis and other more common mental health disorders such as depression and anxiety is confusing, because cannabis is also sometimes used to relieve symptoms of depression and anxiety.
However, while cannabis may seem to help ease depression before the effects of the drug wear off, after that, smoking cannabis may make depression worse. Those who use cannabis have been shown to have higher levels of depression and depressive symptoms than those who do not use cannabis (Lev-Ran et al., 2014; Pacek et al., 2013). This risk may increase for users who use both cannabis and alcohol (Pacek et al., 2013).
Although results are mixed, there is some research to suggest that cannabis use in adolescence, particularly frequent or heavy use, is associated with the development of anxiety disorder in young adulthood (Degenhardt et al., 2013). Studies have also found that frequent cannabis use in teenagers predicts depression, as well as anxiety disorder, later in life as well, with daily users carrying the highest risk. Young women appear to be more likely to experience this effect (Patton et al., 2002). Use of cannabis in adolescence has also been correlated with the development of suicidal ideation, certain personality disorders, and interpersonal violence. Younger age of initiation increases the risk of developing all of these mental health disorders later (Copeland et al., 2013).
Are some people more at risk than others?
Generally speaking, those who start smoking cannabis earlier (early adolescence) and smoke heavily are more likely to experience negative consequences. This may in turn lead to mental health problems, but also lead to more general life problems, like conflict at home or school / work, financial problems and memory problems. For more information on cannabis and adolescents, see our Adolescents factsheet.
If you seem to be frequently depressed or anxious after smoking cannabis, or if you are having suicidal thoughts after smoking, cannabis may not be safe for you. Pay attention to your body and emotional responses. Again, for anyone who has a genetic vulnerability or existing mental health issues, cannabis should be avoided.
What help is available?
Drug and alcohol services and mental health services are available in most areas and ideally, a coordinated approach that will tackle both issues at the sample time can be arranged. Often medication is available to assist with symptoms and this can be managed by a skilled general practitioner. Additionally there are some psychologists and social workers who may have specific training in this area.
For specific information on where to get help — on the phone, the web, or in person — please visit our page about Where to Get Help.
References
- Arseneault L, Cannon M, Poulton R, et al. Cannabis use in adolescence and risk for adult psychosis: longitudinal prospective study. BMJ 2002;325:1212-3. View abstract
- Copeland J, Rooke S, Swift W. Changes in cannabis use among young people: Impact on mental health. Curr Opin Psychiatry 2013;26:325-329. View abstract
- Degenhardt L, Coffey C, Romaniuk H, Swift W, Carlin JB, Hall WD, Patton GC. The persistence of the association between adolescent cannabis use and common mental disorders into young adulthood. Addiction. 2013 Jan;108(1):124-33. View abstract
- Lev-Ran S, Roerecke M, Le Foll B, et al. The association between cannabis use and depression: A systematic review and meta-analysis of longitudinal studies. Psychol Med 2014 ;44(4):797-810. View abstract
- Pacek LR, Martins SS, Crum RM. The bidirectional relationships between alcohol, cannabis, co-occurring alcohol and cannabis use disorders with major depressive disorder: Results from a national sample. J Affect Discord 2013;148(2-3):188-95. Free online
- Parakh P, Basu D. Cannabis and psychosis: Have we found the missing links? Asian J Psychiatr 2013;6(3):281-7. View abstract
- Patton GC, Coffey C, Carlin JB, et al. Cannabis use and mental health in young people: Cohort study. BMJ 2002;324(7374):1195-8. View abstract
- Power RA, Verweij KJ, Zuhair M, et al. Genetic predisposition to schizophrenia associated with increased use of cannabis. Mol Psychiatry 2014;19(11):1201–1204. Free online
- Sewell RA, Ranganathan M, D’Souza DC. Cannabinoids and psychosis. Int Rev Psychiatry 2009;21(2):152-62. View abstract
Updated 2017. This information adapted with permission from the National Cannabis Prevention and Information Centre in Australia.