Mo. Rev. Stat. § 105.1105

105.1105. First conviction of employee for use of drugs, certified drug abuse treatment and education requirement — failure to comply, suspension and dismissal — employee in compliance to be returned to position or comparable status. — Any public employee who is convicted, pleads guilty, or pleads nolo contendere for the first time, under the laws of this state, the United States or any other state, of any criminal offense involving the use of a controlled substance, marijuana or other dangerous drug as such substances are defined in chapter 195 shall be required to show evidence of completion of a drug abuse treatment and education program certified by the state. If the public employee refuses to participate in a drug abuse treatment program or if he fails to complete such program within six months of his public employer becoming aware of the conviction, the public employee shall be suspended from his public employment until such time as he shows evidence of completion of or shows evidence of enrollment and continuing progress in a certified drug abuse treatment and education program. Notwithstanding the provisions of section 36.370 , such suspension shall be for no more than three months, after which time, if the public employee has failed to complete or has failed to show evidence of continuing progress in a drug abuse treatment and education program, he shall be dismissed from his public employment. After all requirements of the suspension period have been fulfilled by the public employee, he shall be returned to his former position with the public employer or, if such position is no longer available, he shall be placed in a position of comparable status as his former position prior to suspension.

(L. 1993 S.B. 67 § 3)