195.180. 1. A person may lawfully possess or have under his control a controlled substance if such person obtained the controlled substance directly from, or pursuant to, a valid prescription or order of a practitioner while acting in the course of a practitioner's professional practice or except as otherwise authorized by sections 195.005 to 195.425.
2. In any complaint, information, or indictment, and in any action or proceeding brought for the enforcement of any provision of sections 195.005 to 195.425, it shall not be necessary to negative any exception, excuse, proviso, or exemption, contained in sections 195.005 to 195.425, and the burden of proof of any such exception, excuse, proviso or exemption, shall be upon the defendant.
(RSMo 1939 § 9849, A.L. 1989 S.B. 215 & 58)
Missouri General Assembly