195.180
NARCOTIC NEWS
Drug Law in Missouri 195.180
Lawful possession, when--burden of proof of any exception or exemption
upon defendant
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)
Google