(a) No person shall prescribe or order the dispensing of a dangerous drug, except a registered practitioner who is:

(1) Licensed or otherwise authorized by this state to prescribe dangerous drugs;

(2) Acting in the usual course of his professional practice; and

(3) Prescribing or ordering such dangerous drug for a legitimate medical purpose.

(b) Any person violating subsection (a) of this Code section shall be guilty of a misdemeanor.