Relationship of zolpidem and cancer risk: a Taiwanese population-based cohort study.

OBJECTIVE To evaluate the relationship between the use of zolpidem and subsequent cancer risk in Taiwanese patients. METHODS We used data from the National Health Insurance system of Taiwan to investigate whether use of zolpidem was related to cancer risk. For the study cohort, we identified 14,950 patients who had received a first prescription for zolpidem from January 1, 1998, through December 31, 2000. For each zolpidem user, we selected randomly 4 comparison patients without a history of using zolpidem who were frequency-matched by sex, age, and year of the index date. Incidence rates of all cancers and selected site-specific cancers were measured by the end of 2009, and related hazard ratios (HRs) and 95% confidence intervals (CIs) of the cancer were measured as well. RESULTS The risk of developing any cancer was greater in patients using zolpidem than in nonusers (HR, 1.68; 95% CI, 1.55-1.82). The stratified analysis showed that the overall HR for high-dosage zolpidem (≥300 mg/y) was 2.38. The site-specific cancer risk was the highest for oral cancer (HR, 2.36; 95% CI, 1.57-3.56), followed by kidney cancer, esophageal cancer, breast cancer, liver cancer, lung cancer, and bladder cancer (HR, 1.60; 95% CI, 1.06-2.41). Men were at higher risk than women. CONCLUSION This population-based study revealed some unexpected findings, suggesting that the use of zolpidem may be associated with an increased risk of subsequent cancer. Further large-scale and in-depth investigations in this area are warranted.