Cannabis use can increase the risk of mental health problems, especially in young people. This risk increases with frequency and amount of cannabis use. The frequent or even occasional use of cannabis can cause anxiety, depression, paranoia and psychosis in those people who have a vulnerability to mental health problems. People who use cannabis in their teens may also have an increased risk of developing schizophrenia. This risk also increases with frequency and amount of cannabis use.
The 2007 National Drug Strategy Household Survey found that in WA:
- 9.6% of WA recent cannabis users aged 15 to 25 years were diagnosed and/or treated for depression in the last twelve months compared to 3.6% of non-recent cannabis users aged 15–25 years.
- 3.0% of WA recent cannabis users aged 15 to 25 years were diagnosed and/or treated for anxiety in the last twelve months compared to 1.5% of non-recent cannabis users aged 15–25 years.
- 4.2% of WA recent cannabis users aged 15 to 25 years were diagnosed and/or treated for an eating disorder in the last twelve months compared to 0.5% of non-recent cannabis users aged 15–25years.
- 50.4% of WA recent cannabis users aged 15 to 25 years reported to be in a moderate-very high level of psychological distress compared to 37.2% of non-recent cannabis users (using Kessler 10).
- 7.2% of recent cannabis users aged 15 to 25 years have been diagnosed and/or treated for a sexually transmitted disease in the last twelve months compared to 0.7% of non-recent cannabis users aged 15 to 25 years.
Read the 2007 National Drug Strategy Household Survey findings.
There is also a growing body of research that indicates cannabis causes significant harm to the community, particularly in relation to physical and metal health, and wellbeing.
A recent study found that people in the general population who have ever used cannabis are 1.4 times more likely to have a psychotic outcome and that there is a dose-response relationship that exists between regular (daily/weekly) cannabis use and a psychotic outcome. Read the full article.
The global cannabis commission report suggests that cannabis use and psychotic symptoms are associated in general population surveys and exist even after adjusting for confounders. People who have used cannabis at least once before the age of 18 are 2.4 times more likely to be diagnosed with schizophrenia than those who had not, with this risk increasing with the frequency of cannabis use. The report also estimates that 13% of all schizophrenia cases would be averted if all cannabis use was prevented.
The report also found that under cannabis intoxication, short term memory, attention, motor skills, reaction time and skilled activities are impaired. MRI techniques using cognitive tasks have shown diminished activity in the brains of regular cannabis users compared to non-users, even up to 28 days abstinence. Regular cannabis users also have lower resting brain blood flow compared to controls (particularly in the lower prefrontal cortex and cerebellum). However, the long term implications of this are not known. Individuals who have used cannabis for more than ten years and reportedly smoked five or more joints a day had reduced volumes in their hippocampus and amygdale (memory and emotion areas).
A representative sample of Australians aged 13 to 17 years that had used cannabis were also three times more likely to meet the diagnostic criteria for depression compared to non-users. More than one in three (36%) of adolescents who had used cannabis ten or more times by the age of 15 to 16 years, met diagnostic criteria for a mood disorder compared to one in ten (11%) of those who had never used cannabis. By the age of 30 years, individuals who had ever met diagnostic criteria for depression were 2.3 times more likely to report weekly cannabis use.
Read the full The global cannabis commission report.
Evidence also suggests that cannabis use can play a causal role in the development of psychosis in some patients. It is also suggested that there is a relationship between cannabis use and the earlier onset of psychotic illness. This study that took in data from 20,000 patients with a psychotic illness has found that the age at onset of psychosis for cannabis users was 2.70 years younger than for non-users, and for those with broadly defined substance use, the age at onset of psychosis was 2.00 years younger than for non-users. Read more about this study.
A recent study also found that regular cannabis users have an increased risk of using other drugs compared to occasional users, while those who had never used cannabis were least likely to begin using any other drugs. Those who had never used cannabis were also most likely to give up tobacco smoking and high-risk drinking in their 20s. The study also found that cannabis users who quit using in their 20s were a third to half as likely to use other illicit drugs then occasional users. Read more about this study.
Cannabis use can decrease cognitive and behavioural performance that can increase the risk of injury. Cannabis users are nearly twice as likely to report injury from all causes including self inflicted injury, motor vehicle accidents, and assaults compared to non-users. Cannabis users are twice as likely to report being involved in a motor vehicle accident than drivers who do not use cannabis. The report also found that regular cannabis smokers are more likely to report chronic bronchitis, pneumonia and respiratory infections than non-smokers and are 5.7 times more likely to be diagnosed with lung cancer. Older regular cannabis users are also 4.8 times more likely to have an increased risk of myocardial infarction in the first hour after consumption. Read more about this report.
Reports from the National Cannabis Prevention and Information Centre (NCPIC) suggest that cannabis use has been shown to make psychotic symptoms worse in those who already have a psychotic disorder. Evidence suggests that cannabis may somehow trigger schizophrenia in those who are already at risk of developing the disorder.
Although cannabis has a sedating effect which makes the drug less likely to cause violence in users compared to other drugs such as alcohol and stimulants, sometimes when cannabis is used it can cause fear, anxiety, panic or paranoia, which can result in an aggressive outburst. Violent outbursts are more likely to occur among people who use cannabis regularly compared to those who use it occasionally or not at all. However, it is also possible that people with violent tendencies can have a range of other psychosocial problems, and therefore are more likely to use cannabis. In addition, cannabis withdrawal can cause irritability which can lead to abusive or aggressive behaviour.
The reports also show that there is concern around smoking cannabis compared to smoking tobacco which is due to cannabis being generally smoked with a prolonged and deeper inhalation than tobacco. People also tend to smoke cannabis with a shorter butt length and at a higher combustion temperature. This results in a ~five times greater carboxyhaemoglobin concentration, a three fold greater amount of tar inhaled and retention of a third more tar in the respiratory tract.
NCPIC reports also show that one in ten individuals who have ever used cannabis are at risk of dependence. This risk increases to one in six with those who initiate cannabis in adolescence, and increases again to between 1 to 2 to 3 for daily cannabis users. People who are dependent on cannabis are also at an increased risk of short-term memory impairments, mental health problems and respiratory diseases (if smoked). Cannabis consumption also increases the risk of cardiovascular disease, impaired respiratory function, and premature births. Find out more at http://ncpic.org.au