A medical psychologist is a clinical psychologist who also has a post doctoral masters in clinical psychopharmacology. Jobs and salary are highly dependent on location.
Most medical psychologists start out in clinical psych programs and take health or medical specialization/concentration courses then after graduating pursue a masters/post-doctoral program in psychopharm. Many given their specialized interests have health or medical related practicums, internships, and residencies. You learn more about the physiological/medical (physical exams, labs, meds) side of psychology and in a handful of states (if you meet the psychopharm requirements) can be licensed to prescribe. Kind of sort of like a PA (but different) with a doctorate in psychology. ABPP board certifies health psych, where AMP board certifies med psychologists.
To throw another term into the mix.. clinical health psychologists have clinical training and specialized training and/or experience in areas such as health promotion, disease prevention, adjustment to chronic or life-threatening illnesses, etc. They're more likely to collaborate with prescribing clinicians than to write prescriptions themselves.