BACKGROUND: To determine use and investigate factors associated with use of hypnotics the first year after a diagnosis with breast cancer.

MATERIAL AND METHODS: A retrospective registry based cohort study linking clinical data from the Danish Breast Cancer Group with the National Prescription Drug Database and other health and administrative registries. We included 26 082 women diagnosed with early breast cancer as first time primary cancer during 1996-2006. Use of hypnotics was measured as redeemed prescriptions in the first year after diagnosis of early breast cancer. Prior use of hypnotics was defined as one or more prescriptions of hypnotics 13 months to 1 month before diagnosis, and chronic use was defined as four or more prescriptions. Hazard ratios (HRs) for clinical variables, treatment-related factors and sociodemographic factors were calculated.

RESULTS: Among women with no prior history of hypnotic use, 17% became new users with 4% on a chronic level. Among prior users, 82% continued their use with one or more prescriptions of hypnotics and 15% increased their use to a chronic level. Significantly increased hazard ratios for use of hypnotics were seen with increasing age [age 50-59 years: HR 1.43 (95% CI 1.31-1.57), age 60-69: HR 1.57 (95% CI 1.44-1.71)], increasing number of tumor positive lymph nodes [1-3 lymph nodes: HR 1.12 (95% CI 1.05-1.09), 4-9 lymph nodes: HR 1.11 (95% CI 1.02-1.29)], chemotherapy [HR 1.25 (95% CI 1.12-1.39)], somatic comorbidity [HR 1.31 (95% CI 1.21-1.42)] and use of antidepressants the year before breast cancer diagnosis [HR 1.97 (95% CI 1.85-2.10)].

CONCLUSION: This study detected a group of patients at great risk for initiating and increasing use of hypnotics and preventive and prophylactic mechanism should be investigated and initiated when this group of patients is seen in the clinical setting.