You have to have a lot of physical pain and a specialist who doesn't know what BP means. Or pretend you have SZ. Emphasis: schizoaffective disorder (specialist: "I'm a doctor so I'm not gonna ask what that means, how hard can it be, sounds like schizophrenia. It's probably fine.").

Drug dealers may have heroin as well as morphine. Heroin is such a hassle, so I'd use morphine.