Dispensed drugs and multiple medications in the Swedish population: an individual-based register study.

Background: Multiple medications is a well-known potential risk factor in terms of patient's health. The aim of the present study was to estimate the prevalence of dispensed drugs and multiple medications in an entire national population, by using individual based data on dispensed drugs.

Methods: Analyses of all dispensed out-patient prescriptions in 2006 from the Swedish prescribed drug register. As a cut-off for multiple medications, we applied five or more different drugs dispensed (DP >or= 5) at Swedish pharmacies for a single individual during a 3-month, a 6-month, and a 12-month study period. For comparison, results were also calculated with certain drug groups excluded.

Results: 6.2 million individuals received at least one dispensed drug (DP >or= 1) during 12 months in 2006 corresponding to a prevalence of 67.4%; 75.6% for females and 59.3% for males. Individuals received on average 4.7 dispensed drugs per individual (median 3, Q1-Q3 2-6); females 5.0 (median 3, Q1-Q3 2-7), males 4.3 (median 3, Q1-Q3 1-6).The prevalence of multiple medications (DP >or= 5) was 24.4% for the entire population. The prevalence increased with age. For elderly 70-79, 80-89, and 90-years, the prevalence of DP >or= 5 was 62.4, 75.1, and 77.7% in the respective age groups. 82.8% of all individuals with DP >or= 1 and 64.9% of all individuals with DP >or= 5 were < 70 years. Multiple medications was more frequent for females (29.6%) than for males (19.2%). For individuals 10 to 39 years, DP >or= 5 was twice as common among females compared to males. Sex hormones and modulators of the genital system excluded, reduced the relative risk (RR) for females vs. males for DP >or= 5 from 1.5 to 1.4. The prevalence of DP >or= 1 increased from 45.1 to 56.2 and 67.4%, respectively, when the study period was 3, 6, and 12 respectively months and the corresponding prevalence of DP >or= 5 was 11.3, 17.2, and 24.4% respectively.

Conclusion: The prevalence of dispensed drugs and multiple medications were extensive in all age groups and were higher for females than for males. Multiple medications should be regarded as a risk in terms of potential drug-drug interactions and adverse drug reactions in all age groups.