Paul John Hanzlik was born in Shueyville, Iowa, on July 24, 1885. He obtained his Ph.G. (Graduate in Pharmacy) degree from the State University of Iowa in 1902. In 1908 he obtained an A.B. and a Ph.C. (Pharmaceutical Chemist) degree from the University of Illinois. His A.M. (1911) and M.D. (1912) degrees were received from Cleveland's Western Reserve University. After graduation from medical school, Dr. Hanzlik served briefly as a demonstrator in pharmacology at Western Reserve University, and then spent a period of study abroad, at the Pharmacological Institute and Physico-Chemical-Biological Institute at the University of Vienna. Upon his return, Dr. Hanzlik became associated with the Stanford medical school, first as an instructor (1913-1915), then as an associate instructor (1915-1917), assistant professor (1917-1920) and associate professor (1920-1921). In 1921 he was named professor of pharmacology at Stanford, a position he held until his retirement in 1950.

During World War I he served as a captain in the U.S. Army's Medical Corps, attached to the Chemical Warfare Service; it is possible that here he met Chauncey Leake, who would later sit on the same committee of San Francisco Department of Health consultants which developed the Handbook of accepted remedies ... The spiral-bound Handbook went into at least three editions by 1940.

Dr. Hanzlik was a member of many professional organizations, such as the American Medical Association, the American Physiological Society, the Society of Pharmacology and Experimental Therapeutics, the Society of Experimental Biology and Medicine, the California Academy of Medicine, and the California Medical Association. He was a fellow of the American College of Physicians and an honorary fellow of the American College of Dentists. He was author or co-author of a number of publications, including Actions and uses of the salicylates and cinchophen in medicine (1927) and Fundamentals of experimental pharmacology (1928, 1939). He helped edit the 1930 and 1931 Lane lectures on experimental pharmacology, and published a number of articles on this topic.