This study uses data from August 2006 to July 2007 to determine the distribution of psychotropic drug prescriptions by medical specialty.  The authors find that 59 percent of psychotropic prescriptions were written by general practitioners, 23 percent by psychiatrists and 19 percent by other physicians. 

Mark, T. L., Levit, K. R., Buck, J. A. (2009). Psychotropic Drug Prescriptions by Medical Specialty. Psychiatric Services, 60: 1167. DOI: 10.1176/appi.ps.60.9.1167 http://psychservices.psychiatryonline.org/cgi/pdf_extract/60/9/1167 

Authors: Tami L. Mark, Katharine R. Levit, Jeffrey A. Buck.