Mo. Rev. Stat. § 105.1108

Any public employee who is convicted, pleads guilty, or pleads nolo contendere for a second or subsequent 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 dismissed from his public employment and shall be ineligible for other public employment for a period of two years from the most recent date of conviction. Subsequent employment with a public employer after the two-year period shall be conditioned upon the showing of evidence of completion of a state certified drug abuse treatment and education program.