Mo. Rev. Stat. § 199.240
No person committed to a facility designated by the department of health and senior services under sections 199.170 to 199.270 shall be required to submit to medical or surgical treatment without his consent, or, if incapacitated, without the consent of his legal guardian, or, if a minor, without the consent of a parent or next of kin.
(L. 1961 p. 518 § 9, A.L. 1971 H.B. 581, A.L. 1983 S.B. 44 & 45, A.L. 1985 S.B. 19, A.L. 1996 S.B. 540, A.L. 2010 S.B. 1007)