Dr. Hjorthøj is internationally recognized as an expert within the area of dually diagnosed substance use disorder and psychiatric disorders. Dr. Hjorthøj has a special focus on the area of cannabis and psychosis and has published numerous highly cited studies in the field. Dr. Hjorthøj has worked tirelessly to shed light on the mental health sequalae of cannabis use, both in relation to developing mental illness and in people already suffering from mental illness. In addition to his focus on cannabis and schizophrenia, Dr. Hjorthøj is currently working to expand our knowledge on substance-induced psychosis in general and cannabis-induced psychosis in particular. Finally, Dr. Hjorthøj is also involved in research into whether cannabinoids, in particular CBD, are safe and efficacious for various disorders.