An anonymous reader writes with news of a study out of the Netherlands (abstract) about the link between psychosis and marijuana use. The researchers wanted to examine what caused the relationship — was marijuana use leading to psychosis, or did those suffering from psychosis have a higher tendency to seek out marijuana? As it turns out, they found evidence for both. From the article: "... using pot at 16 years old was linked to psychotic symptoms three years later, and psychotic symptoms at age 16 were linked to pot use at age 19. This was true even when the researchers accounted for mental illness in the kids' families, alcohol use and tobacco use. Griffith-Lendering said she could not say how much more likely young pot users were to exhibit psychotic symptoms later on. Also, the new study cannot prove one causes the other. Genetics may also explain the link between pot use and psychosis, said Griffith-Lendering."