A considerable proportion of HCPs were unfamiliar with key terms related to thiopurine drugs and their mechanisms: 111 (68.9%) were unaware of “thiopurine drugs,” 139 (86.3%) were unfamiliar with the TPMT gene, 76 (47.2%) did not know about TPMT enzyme deficiency, and 69 (42.9%) were unaware of “testing strategies to assess TPMT activity.” Nevertheless, a majority of respondents, 89 (55.3%), correctly recognized thiopurine ADRs, although only 34 (21.1%) knew that these ADRs include myelosuppression, leukopenia, or hepatotoxicity. The gene discussed is TPMT; the disease is myelosuppression.