What does Missouri prohibit in med spa advertising?

Short answer
The cited rules do not settle this — they set one limit: claiming a disease, ailment or infirmity can be cured by any method, treatment, medicine or device is misrepresentation and disciplinable, and deceptive advertising of merchandise is unlawful.

Three subparagraphs of Missouri’s omnibus discipline ground — misconduct, fraud, misrepresentation, dishonesty, unethical conduct or unprofessional conduct in the performance of the functions or duties of any profession licensed or regulated by CHAPTER 334 — bear directly on how a med spa sells: misrepresenting that any disease, ailment or infirmity can be CURED by a method, procedure, treatment, medicine or device; obtaining or attempting to obtain any fee, charge, tuition or other compensation by fraud, deception or misrepresentation, including willfully and continually overcharging or overtreating patients or charging for visits that did not occur; and attempting, directly or indirectly, by intimidation, coercion or deception, to obtain or retain a patient or to discourage the use of a second opinion or consultation. Outside the board, the Merchandising Practices Act declares deception, fraud, false pretense, false promise, misrepresentation, unfair practice or the concealment, suppression or omission of any material fact in connection with the sale or advertisement of merchandise an unlawful practice, and the attorney general may seek an injunction in circuit court against it.