Researchers from the Norwegian Institute of Public Health (NIPH), together with colleagues from Virginia Commonwealth University, examined the relationship between cannabis and psychosis using psychiatric interviews of Norwegian twins. The interviews reveal whether the twins had symptoms of psychosis and cannabis abuse.
Genetic factors influence both cannabis abuse and psychosis and the same genes may lead to an increased risk for both problems.
“The relative importance of genes in the causes of a disease is known as heritability, and we know from previous studies at the NIPH that cannabis abuse is very heritable, explains Eivind Ystrom, senior researcher at NIPH.
“In order to determine whether cannabis abuse can lead to psychosis, it is important to account for genetic risk,” he adds.
The researchers therefore tested both the hypotheses that cannabis use causes psychotic symptoms and that psychotic symptoms lead to cannabis abuse.
Abuse increased the risk by 3.5 times
The hypothesis best suited to the data was that cannabis abuse caused symptoms of psychosis. Within a twin pair, the twin with symptoms of cannabis abuse had a 3.5 times higher risk of developing symptoms of psychosis compared with the twin who did not have symptoms of cannabis abuse.
Read full report here: and Full Research Paper included below at end of this post
Full Research Paper:
GeneticTwinStudyOnCannabisPsychosis2016.pdf (392.0 KB)