Factsheet published June 1, 2008. Updated June 1, 2012.
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).
Psychoses refers to a group of mental illnesses where people experience difficulty in distinguishing what is real and what is not real. Someone suffering from a psychosis might hear voices or see/taste/smell things that are not really there (hallucinations), or have beliefs that are not true (delusions). Hallucinations and delusions are usually accompanied by confused thinking and speech, making it difficult for other people to understand the person and for the person to function in life. Schizophrenia is the best known of the group and is one type of psychosis.
There have been reports of people experiencing psychotic symptoms after smoking a lot of cannabis or more cannabis than they are used to. This is called drug-induced psychosis. It is uncommon and the symptoms, although frightening at the time, go away when cannabis use is stopped.
Does smoking cannabis cause schizophrenia?
Evidence suggests that using cannabis may trigger schizophrenia in those who are already at risk of developing the disorder, and they may experience psychosis earlier. Any use of cannabis can double the risk of schizophrenia in those who are vulnerable, and bring on a first episode up to two and a half years earlier. Those with a vulnerability to developing schizophrenia, such as having a family history of the illness, should be strongly advised against using cannabis for this reason. Cannabis has been clearly shown to make psychotic symptoms worse in people who already have a psychotic disorder such as schizophrenia. 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 often used to relieve symptoms of these conditions.
Although some people say the use of cannabis alleviates their symptoms of depression, there is evidence that smoking cannabis may make depression worse. People who use cannabis have been shown to have higher levels of depression and depressive symptoms than those who do not use cannabis. There is growing evidence to suggest that cannabis use, particularly frequent or heavy use, predicts depression later in life. Young women appear to be more likely to experience this effect.
Cannabis can lead to symptoms of anxiety, such as panic, in the short-term, which a fifth of users experience, but there is a lack of evidence pointing to cannabis as an important risk factor for chronic anxiety disorders such as panic disorder or obsessive compulsive disorder.
Are some people more at risk than others?
Generally speaking, people who start smoking cannabis at a younger age (early adolescence) and smoke heavily are more likely to experience negative consequences. This may in turn lead to mental health problems, but may also lead to more general life problems, like conflict at home or school/work, financial problems and memory problems.
Importantly, if someone has a genetic vulnerability (i.e. close family with depression, psychosis, bipolar disorder or anxiety) or has an existing mental health issue, cannabis should be avoided.
What help is available?
A good place to start is to visit your GP who can work with you to develop a mental health care plan. Rebates for services provided by healthcare professionals may be available through Medicare or your private health insurer. Psychologists, occupational therapists, social workers and nurses may have specific training to provide therapy or counselling for people with cannabis and mental health problems.
The doctor can refer you to either drug and alcohol services and/or mental health services which are available in most areas of Australia. Ideally they will use a coordinated approach that will tackle both issues at the same time. Treatment usually involves counselling and in some cases medicine is prescribed to assist with symptoms of mental health problems. This should be managed by a general practitioner (with specialist training if possible) or a psychiatrist.