Moore (defendant) was convicted for possession of heroin. At trial, the prosecution conceded that Moore was an addict. There was conflicting evidence as to whether he was engaged in the trafficking of heroin. The trial court refused to permit defendant’s expert witness to testify on the nature of Moore’s heroin addiction and declined to instruct the jury that a non-trafficking heroin addict could not be convicted under the law. Moore was found guilty and appealed, arguing the conviction was improper because of his inability to control himself and refrain from using heroin.