Cannabis contains over 100 different
cannabinoid compounds, many of which have displayed
psychoactive effects. The most distinguished cannabinoids are
tetrahydrocannabinol (THC) and
cannabidiol (CBD), with THC being the primary psychoactive agent.
Chronic psychosis and schizophrenia spectrum disorders According to the National Academies of Sciences, Engineering and Medicine, there is substantial evidence of a statistical association between cannabis use and the development of
schizophrenia or other chronic psychoses, with the highest risk potentially among the most frequent users. Medical evidence strongly suggests that the long-term use of cannabis by people who begin use at an early age display a higher tendency towards mental health problems and other physical and development disorders, although a causal link could not be proven by the available data. The risks appear to be most acute in adolescent users. Nevertheless, some researchers maintain there exists "a strong association" between schizophrenia and cannabis use, while cannabis use alone does not predict the transition to subsequent psychiatric illness. Many factors are involved, including genetics, environment, time period of initiation and duration of cannabis use, underlying psychiatric pathology that preceded drug use, and combined use of other psychoactive drugs. The temporal relationship between cannabis and psychosis was reviewed in 2014, and the authors proposed that "[b]ecause longitudinal work indicates that cannabis use precedes psychotic symptoms, it seems reasonable to assume a causal relationship" between cannabis and psychosis, but that "more work is needed to address the possibility of gene-environment correlation." In 2016 a meta-analysis was published on associations studies covering a range of dosing habits, again showing that cannabis use is associated with a significantly increased risk of psychosis, and alleged that a
dose–response relationship exists between the level of cannabis use and risk of psychosis. The risk was increased 4-fold with daily use, though the analysis was not adequate to establish a causal link. Another 2016 meta-analysis found that cannabis use only predicted transition to psychosis among those who met the criteria for abuse of or dependence on the drug. '' flower with visible
trichomes Another 2016 review concluded that the existing evidence did not show that cannabis caused psychosis, but rather that early or heavy cannabis use were among many factors more likely to be found in those at risk of developing psychosis. An opposing view was expressed in 2016, in a study that regarded the epidemiologic evidence on cannabis use and psychosis was strong enough "to warrant a public health message that cannabis use can increase the risk of psychotic disorders," but also cautioning that additional studies are needed to determine the size of the effect. Such a public health message was subsequently issued in August 2019 by the
Surgeon General of the United States. The review also stated "If the association between cannabis and schizophrenia is causal and of the magnitude estimated across studies to date, this would equate to a schizophrenia lifetime risk of approximately 2% in regular cannabis users (though risk for broader psychotic outcomes will be greater). This implies that about 98% of regular cannabis users will not develop schizophrenia...[and that] risk could be much greater in those at a higher genetic risk, or in those who use particularly potent strains of cannabis. Expressed in terms of
odds ratio, another study found that "Daily cannabis use was associated with increased odds of psychotic disorder compared with never users (adjusted odds ratio [OR] 3.2, 95% CI 2.2–4.1), increasing to nearly five-times increased odds for daily use of high-potency types of cannabis (4.8, 2.5–6.3)." To calculate what the increased odds ratio For some locations, this translates into a substantial
population attributable risk, such that "assuming causality, if high-potency cannabis types were no longer available, then 12% of cases of first-episode psychosis could be prevented across Europe, rising to 30% in London and 50% in Amsterdam." However, a 2004 study noted that general population statistics show no increase in psychosis incidence rates in any developed country over the last 50 years, despite a five-fold increase in cannabis use rates. The study noted that "cannabis use appears to have increased substantially amongst young people over the past 30 years, from around 10% reporting ever use in 1969–70, to around 50% reporting ever use in 2001, in Britain and Sweden. If the relation between use and schizophrenia were truly causal and if the relative risk was around five-fold then the incidence of schizophrenia should have more than doubled since 1970. However population trends in schizophrenia incidence suggest that incidence has either been stable or slightly decreased over the relevant time period." Of note, cannabis with a high THC to CBD ratio produces a higher incidence of psychological effects. CBD may show antipsychotic and neuroprotective properties, acting as an antagonist to some of the effects of THC. Studies examining this effect have used high ratios of CBD to THC, and it is unclear to what extent these laboratory studies translate to the types of cannabis used by real life users. Research has suggested that CBD can safely reduce some symptoms of psychosis in general. A 2014 review examined psychological therapy as add-on for people with schizophrenia who are using cannabis:
Transient psychosis As of 2017 there was clear evidence that long-term use of cannabis increases the risk of psychosis, regardless of
confounding factors, and particularly for people who have genetic risk factors. Even in those with no family history of psychosis, the administration of pure THC in clinical settings has been demonstrated to elicit transient psychotic symptoms.
Depersonalization/derealization symptoms Cannabis use may precipitate new-onset panic attacks and depersonalization/derealization symptoms simultaneously. The association between cannabis use and
depersonalisation/derealisation disorder has been studied. Depersonalization is defined as a dissociative symptom in which one feels like an outside observer with respect to one's thoughts, body, and sensations. While derealization is marked by feelings of unreality and detachment from one's surroundings, such that one's environment is experienced as remote or unfamiliar. Some individuals experiencing depersonalisation/derealisation symptoms prior to any cannabis use have reported the effects of cannabis to calm these symptoms and make the depersonalisation/derealisation disorder more manageable with regular use.
Depressive disorder Less attention has been given to the association between cannabis use and
depression, though according to the
Australian National Drug & Alcohol Research Centre, it is possible this is because cannabis users who have depression are less likely to access treatment than those with psychosis. The findings on marijuana's relationship to depressive disorder are scattered, showing that cannabis use has benefits, but can also be detrimental to overall mental health. However, sufficient evidence exists showing reductions in cannabis use improve anxiety, depression, and sleep quality. A 2017 review suggests that cannabis has been shown to improve the mood of depression-diagnosed patients. This is due to a desire to alleviate the symptoms of these experiences through marijuana use. Chronic users who use for anxiolytic purposes will even develop dependencies on cannabis, making it difficult to cope with anxiety when the drug is absent. Teenage cannabis users show no difference from the general population in incidence of
major depressive disorder (MDD), but an association exists between early exposure coupled with continued use into adult life and increased incidence of MDD in adulthood. Among cannabis users of all ages, there may be an increased risk of developing depression, with heavy users seemingly having a higher risk. Heavy marijuana use in adolescence has also been associated with deficits in cognition. A recent study assessing changes in neuropsychological functioning resulting from long-term cannabis use followed a group of adolescents (ages 12-15 at baseline) over a 14-year period. Researchers found that more days of use were correlated with decreases in inhibitory control, and visuospatial ability. Contrary to existing cross-sectional studies showing marijuana use in adolescence is associated with poor cognitive functioning, there were no associations between long-term cannabis use and memory and processing speed. While this study showed no correlations between memory and cannabis use, others have found that there is. A February 2019
systematic review and
meta-analysis found that cannabis consumption during adolescence was associated with an increased risk of developing depression and suicidal behavior later in life, while finding no effect on anxiety. A 2023 study in
JAMA Network Open found that even non-disordered recreational cannabis use among U.S. adolescents was associated with a two- to four-fold higher risk of developing psychiatric disorders including depression and anxiety. A 2026 study in
Pediatrics additionally linked any cannabis use among adolescents to poorer academic performance and emotional distress. In a longitudinal study assessing the associations between long term use and mental health in a group of individuals participating in a drug-based treatment for depression, researchers found that, compared to non-users, patients using both medically and non-medically experienced less improvement in depressive symptoms and an increase in suicidal ideation. Additionally, those who used non-medically, were less likely to visit the psychiatrist.
Mania symptoms Mania is a mental illness marked by periods of great excitement or euphoria, delusions, and overactivity. This is common in cannabis users when they hit a point of their high that could lead to paranoia, anxiety, and increased heart rate. Some strains of the drug can have these effects on the individuals that use them, but no effects are guaranteed when used. A case review reported that an adult user had marijuana-induced mania even though they had no previous psychiatric history. However, some participants that have been previously diagnosed with bipolar disorder, had a worsening occurrence with mania symptoms.
Suicidal behavior Adolescent cannabis users show no difference from their peers in
suicidal ideation or rate of suicide attempts, but those who continue to use cannabis into adult life exhibit an increased incidence of both, although multiple other contributory factors are also implicated. although it remains unclear whether regular cannabis use increases the risk of suicide. Cannabis use is a risk factor in suicidality, but suicide attempts are characterized by many additional risk factors including mood disorders, alcohol use, stress, personal problems and poor support. ==Gateway drug hypothesis==