What's the difference between a Medical Psychologist and a Prescribing Psychologist?

The simple answer is nothing and a lot... read on.

A Medical Psychologist can be a:

1-highly trained and licensed psychologist 

• With a Master's in Science in Psychopharmacology
• Psychology license from the Louisiana State Board of Examiners of Psychologists 
• Medical license from the Louisiana State Board of Medical Examiners
• Who prescribes psychotropic medications with frequent consultation in Louisiana

OR

2-highly trained and licensed psychologist  

• With a Doctorate in Psychology
• Board Certified Speciality from the American Board of Psychological Specialties, 

• A Division of the American College of Forensic Examiners

So, prescribing psychologists can ONLY practice in Louisiana, New Mexico, Guam, Native American territories, and some state and Federal departments.

Thanks for reading, 
Dr. Jon Chandler

FYI-A licensed psychologist requires ALL of the following:
1-HS Diploma/GED Equivalent
2-BA/BS
3-MA/MS
4-PsyD/PhD
5-1500 Post-Doctoral Externship hours
6-Passing score on the National and State exam
7-Licensure with a state Board of Psychology

What is a Medical Psychologist?

QUESTION #1:

What is a Medical Psychologist?

Good question!!! 

ANSWER #1:

It does not have the easiest answer...Here is how wikipedia, health-psych and Academy of Medical Psychology define it:

Medical psychology is the application of psychological principles to the practice of medicine for both physical and mental disorders. The American Psychological Association (APA) defines medical psychology as "that branch of psychology that integrates somatic and psychotherapeutic modalities into the management of mental illness and emotional, cognitive, behavioral and substance use disorders". A medical psychologist does not automatically equate with a psychologist who has the authority to prescribe medication.

Medical psychologists apply psychological theories, scientific psychological findings, and techniques of psychotherapy, behavior modification, cognitive, interpersonal, family, and life-style therapy to improve the psychological and physical health of the patient. Clinical psychologists with post doctoral specialty training as medical psychologists are the practitioners with refined skills in clinical observation in of the field of psychology, learning, central nervous system adaptation and change, and adaptation and lifestyle change applying a number of different methods in several different mediums of treatment. Highly qualified and post graduate specialized doctors are trained for service in primary care centers, hospitals, residential care centers, and long-term care facilities and in multidisciplinary collaboration and team treatment. They are trained and equipped to modify physical disease states and the actual cytoarchitecture and functioning of the central nervous and related systems using psychological and pharmacological techniques (when allowed by statute), and to provide prevention for the progression of disease having to do with poor personal and life-style choices and conceptualization, behavioral patterns, and chronic exposure to the effects of negative thinking, choosing, attitudes, and negative contexts.^[1][2]

In Louisiana, the term of medical psychologist refers, in statute, specifically to those psychologists licensed by the Louisiana State Board of Medical Examiners and who are authorized and licensed to prescribe medications. The term mirrors precisely the terminology of the United States Drug Enforcement Administration (DEA). It is important to note that the Division 38 of the American Psychological Association and The Academy of Medical Psychology does not agree or recognize that the term medical psychologist has, as a prerequisite, the ability, certification, or licensure to prescribe medications in the care and management of patients nor should the term be equated with having prescriptive authority.

Medical Psychology: The practice of medical psychology involves an awareness of and training in medical, psychological, and social factors that inform a broad spectrum of services including psychological diagnosis, treatment, consulting about the use of psychotropic medications, and prescribing of psychotropic medication within the scope of the practice of the profession.[3]  

References

1. http://www.health-psych.org/MedPsych.cfm
2. http://en.wikipedia.org/wiki/Medical_psychology
3. http://www.amphome.org/ 

Now, for the layperson: 
It is still a bit confusing but I will attempt to simplify it as much as possible. In general, medical psychology is the application of psychological theory to the practice of mental and medical illnesses. Therefore, in most states, a medical psychologist works in a cross-section between mental and medical practices. This does not necessarily mean they prescribe medications.

In Louisiana (LA), a medical psychologist has met all requirements and has become licensed by the Louisiana Medical Board of Examiners to prescribe psychotropics medications. Said person, will even have a suffix of M.P. for Medical Psychologist.

• Ex-Jon Chandler, Psy.D., M.P. 

In New Mexico (NM) and Guam (GU), the same person described above is called a prescribing psychologist.

In LA, NM, and GU to prescribe psychotropic medications one must have the following:-Completed a doctoral degree in psychology-Provided mental health services as a practicing psychologist-A current license to practice psychology-Completed a Postdoctoral Master's of Science program in Psychopharmacology at an accredited institution (Ex-Alliant International University)-Completed at least three hundred contact areas in neuroscience, pharmacology and psychopharmacology, physiology and pathophysiology, physical and laboratory assessment, and clinical pharmacotherapeutics as part of one’s postdoctoral education
-Pass the national Psychopharmacology Examination for Psychologists (PEP)
-Some states/territories/agencies have additional requirements