<P> A 2014 review said 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 the same year, a review examined psychological therapy as add - on for people with schizophrenia who are using cannabis: </P> <Table> Cannabis reduction: adjunct psychological therapy versus treatment as usual <Tr> <Th> Summary </Th> </Tr> <Tr> <Td> Results are limited and inconclusive because of the small number and size of randomized controlled trials available and quality of data reporting within these trials . More research is needed to explore the effects of adjunct psychological therapy that is specifically about cannabis and psychosis as currently there is no evidence for any novel intervention being better than standard treatment, for those that both use cannabis and have schizophrenia . </Td> </Tr> <Tr> <Td> <Table> <Tr> <Th> show Outcome </Th> <Th> Findings in words </Th> <Th> Findings in numbers </Th> <Th> Quality of evidence </Th> </Tr> <Tr> <Th_colspan="4"> Behavior </Th> </Tr> <Tr> <Td> Frequency of cannabis use (group - based therapy) Follow up: 1 year </Td> <Td> People in the intervention groups scored a little lower compared to people receiving treatment as usual but there was no clear difference between the therapy groups and standard care . This finding is based on data of moderate quality . </Td> <Td> MD 0.1 lower (2.44 lower to 2.24 higher) * </Td> <Td> Moderate </Td> </Tr> <Tr> <Th_colspan="4"> Mental state </Th> </Tr> <Tr> <Td> Average score (PANSS) - positive symptoms Follow up: 12 months </Td> <Td> On average, people receiving cannabis reduction therapy scored lower than people treated with treatment as usual but there was no clear difference between groups . This finding is based on data of moderate quality . </Td> <Td> MD 0.3 lower (2.55 lower to 1.95 higher) * </Td> <Td> Moderate </Td> </Tr> <Tr> <Th_colspan="4"> Quality of life </Th> </Tr> <Tr> <Td> Average score (WHO QOL questionnaire) Follow up: 1 years </Td> <Td> On average, people receiving cannabis reduction therapy scored higher compared to people in the control group receiving treatment as usual . There was, however, no clear difference between the groups and these findings are based on data of moderate quality . </Td> <Td> MD 0.9 higher (1.15 lower to 2.95 higher) * </Td> <Td> Moderate </Td> </Tr> <Tr> <Td> </Td> <Td> No study reported any data on outcomes such as relapse, adverse effects, leaving the study early and information relating to satisfaction with treatment </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> * At present the meaning of these scores in day - to - day care is unclear . </Td> <Td> </Td> <Td> </Td> </Tr> </Table> </Td> </Tr> </Table> <Tr> <Th> Summary </Th> </Tr> <Tr> <Td> Results are limited and inconclusive because of the small number and size of randomized controlled trials available and quality of data reporting within these trials . More research is needed to explore the effects of adjunct psychological therapy that is specifically about cannabis and psychosis as currently there is no evidence for any novel intervention being better than standard treatment, for those that both use cannabis and have schizophrenia . </Td> </Tr>

Side effects of smoking weed for a long time