The maximum security unit of Mathari mainly houses patients found by courts to be criminally insane. Men outnumber women two-to-one among the 200 patients. Among them are severe drug abusers who might not have a criminal record. Health officials reason that the high-security building and its grounds are safer for drug addicts who could easily escape from the low-security wards in other parts of the hospital. Some stay in the maximum security unit for three to six months, Dr Irungu said. "We do a little bit of occupational therapy but not as much as we ought to," he said. Some patients grow sugarcane and other crops inside the high gray concrete walls of the unit and sell their produce in Nairobi.