The history of the Department of Pharmacology dates back to 1890, when the Bhatayakorn School, the first medical school in Thailand, was established at Siriraj Hospital. The initial teaching encompassed both modern and traditional medicine. Initially, pharmacology was taught under the course named SuppakunYa (drug properties), which included drug indications and drug preparations. By 1892, pharmacology had become a part of the basic physiology course instructed by Dr. George B. McFarland.

          In 1922, Prince Mahidol Adulyadej, representing the Thai government, negotiated with the Rockefeller Foundation to elevate medical education in Thailand. The foundation sent Professor E.C. Albritton to improve the teaching of physiology. Upon his appointment as the head of the Department of Physiology, Professor Albritton revised the physiology course content to include biochemistry, physiology, and pharmacology, and introduced a laboratory section.

          In 1924, pharmacology teaching was refined to focus solely on modern medicine. Until 1965, all three subjects were taught under the same course within the Department of Physiology. On November 8, 1965, the Department of Pharmacology became an independent department, with Professor Dr. Ouay Ketusingh serving as its first head. Since then, the Department of Pharmacology has been one of the preclinical departments of Siriraj Medical School, conducting both basic and translational research in pharmacology.