Those subjects who were abusing other substances or suffered from a major psychiatric illness such as recurrent major depression, schizophrenia or bipolar disorder were not included in the study. To corroborate patient interview, case notes were examined and a family member was also used as an informant. As the abuse of drugs other than heroin is uncommon is Southwest China, it was possible to include most subjects interviewed. However, there were some subjects who admitted to excessive alcohol use and these were excluded. The control sample was recruited from college staff, medical students and acute medical inpatients in a general hospital, none of whom had any neurological or psychiatric disorders or a family history of psychiatric or addictive disorders. The control participants did not undergo a formal psychiatric interview but were asked if they had ever been told by a doctor that they suffered from a mental or neurological illness, or had been prescribed drugs or admitted to hospital for such an illness.
