High-potency cannabis and the risk of psychosis
Summary & key facts
Researchers compared 280 people who had just had their first episode of psychosis with 174 healthy local people. They found the two groups were equally likely to have ever tried cannabis and started at about the same age. But people with psychosis were much more likely to be daily users, to have used cannabis for longer than five years, and — among users — far more likely to have used high-potency cannabis such as sinsemilla or “skunk.” The authors say this pattern is consistent with the idea that higher levels of the active ingredient Delta-9-THC may be linked to psychosis, but the study shows an association and does not prove cause and effect.
- The study looked at 280 people who were having their first episode of psychosis and compared them with 174 healthy people from the same area in South London.
- Both groups were about equally likely to have ever tried cannabis, and they started using at similar ages, so simple lifetime use was not different between groups.
- People with psychosis were about six times more likely to be current daily cannabis users than the healthy group. This means heavy daily use was much more common among the patients.
- Those with psychosis were about twice as likely to have smoked cannabis for more than five years. Longer use was more common in the patient group.
- Among people who used cannabis, about 78% of the psychosis group had used high-potency types like sinsemilla or “skunk,” compared with about 37% of the healthy group. Stronger cannabis was much more common in the patient group.
- The authors say these results fit the idea that higher amounts of Delta-9-THC, the main active chemical in cannabis, may increase the risk of psychosis. The study shows an association but does not prove that cannabis caused the psychosis.
- The findings are important for public health because high-potency cannabis has become more available in many countries, making the pattern the researchers observed more relevant to the general population.
Abstract
BACKGROUND: People who use cannabis have an increased risk of psychosis, an effect attributed to the active ingredient Delta 9-tetrahydrocannabinol (Delta 9-THC). There has recently been concern over an increase in the concentration of Delta 9-THC in the cannabis available in many countries. AIMS: To investigate whether people with a first episode of psychosis were particularly likely to use high-potency cannabis. METHOD: We collected information on cannabis use from 280 cases presenting with a first episode of psychosis to the South London & Maudsley National Health Service (NHS) Foundation Trust, and from 174 healthy controls recruited from the local population. RESULTS: There was no significant difference between cases and controls in whether they had ever taken cannabis, or age at first use. However, those in the cases group were more likely to be current daily users (OR = 6.4) and to have smoked cannabis for more than 5 years (OR = 2.1). Among those who used cannabis, 78% of the cases group used high-potency cannabis (sinsemilla, 'skunk') compared with 37% of the control group (OR 6.8). CONCLUSIONS: The finding that people with a first episode of psychosis had smoked higher-potency cannabis, for longer and with greater frequency, than a healthy control group is consistent with the hypothesis that Delta 9-THC is the active ingredient increasing risk of psychosis. This has important public health implications, given the increased availability and use of high-potency cannabis.
