William Jefferson Bleckwenn (July 23, 1895 – January 6, 1965) was an American neurologist, psychiatrist, and military physician, who was instrumental in developing the treatment known as "narcoanalysis" or "narcosynthesis", also known by the lay term "truth serum".

[2] Upon completion of his training, Bleckwenn was asked to join Lorenz and Reese on the staff of WPI, which had by then become part of the UW Department of Neuropsychiatry.

He and Lorenz found that intravenous sodium amytal (amobarbital) was effective in producing a "lucid interval," wherein catatonic patients could converse normally, respond to questions appropriately, move about nimbly, and provide information about their thought processes and backgrounds that would otherwise have been impossible to obtain.

[5] Bleckwenn published his findings on this topic in 1930, in landmark papers in the Wisconsin Medical Journal;[6] the Journal of the American Medical Association (JAMA),[7] and Archives of Neurology & Psychiatry,[8] In the JAMA paper, he stated that "the catatonic patient has shown some extremely interesting and striking responses [to intravenous amytal].

[10] Of those, Fink says "His silent films show the patients as mute, posturing, rigid, with heads raised fixedly from the pillow, and then responding dramatically to multigram doses of amobarbital.

[12] In his text entitled "A Historical Dictionary of Psychiatry," Shorter states that "Some observers view Bleckwenn's procedure as the real beginning of psychopharmacology.

In addition to his administrative command duties, Bleckwenn functioned as a treating neurologist and psychiatrist;[17] he also participated in establishing the "consultant system" of military psychiatric care, under the overall direction of Brig.

With a background of rich experience in the actual handling of nervous and mental casualties in the combat area, he displayed unusual foresight and understanding in organizing the program of treatment for mentally-disabled returnees.

[21] As other psychiatric treatments—such as insulin shock, electroconvulsive therapy, and early psychotropic agents—entered clinical practice in psychiatry, Bleckwenn also took an active role in their use and evaluation.

Bleckwenn is buried at Forest Hill Cemetery in Madison, Wisconsin, with his wife Marion (née Dougan, 1896–1982) and son William Jr.