To be considered a "mental health professional," a person generally must have an M.D., Ph.D. or M.S.W. Some "experts" have an "M.S., P.D." which means they have a Master's degree plus 30 credits -- but have not earned a Ph.D. These people are generally not considered professionals under the law.
The Encyclopedia of Associations (the multi-volume hard cover, Lexis (BUSREF;ENASSC) or Dialog File 114) lists many groups of mental health professionals.