Missouri Revised Statutes Title XXXVIII. Crimes and Punishment; Peace Officers and Public Defenders § 579.107. Lawful possession, when--burden of proof of any exception or exemption upon defendant

1. A person may lawfully possess or have under his or her control a controlled substance if he or she obtained the controlled substance directly from, or pursuant to, a valid prescription or practitioner's order issued in the course of a practitioner's professional practice or except as otherwise authorized by this chapter or chapter 195.

2. In any complaint, information, or indictment, and in any action or proceeding brought for the enforcement of any provision of this chapter or chapter 195, it shall not be necessary to negative any exception, excuse, proviso, or exemption, contained in this chapter or chapter 195, and the burden of proof of any such exception, excuse, proviso or exemption, shall be upon the defendant.