Oral contraceptives and gallbladder disease. Royal College of General Practitioners' oral contraception study.

Abstract

Analyses of the frequency of reporting of gallbladder disease were undertaken as part of the largescale, prospective survey of oral contraceptives (OCs) organized by the Royal College of General Practitioners. A comprehensive account of all data then available was published in May 1974. Data are now reported that were accumulated in the study up to December 1979. 23,000 women using OCs and a similar number of controls who had never used OCs entered the study over 14 months from May 1968 for continuing observation by 1400 general practitioners in the UK. The analyses reported on here were based on women whose 1st report of a diagnosis of gallbladder disease occurred after recruitment to the study. The disease was coded, using the 8th revision of the International Classification of Diseases (ICD) into the 2 main categories of cholelithiasis (ICD 574) and cholecystitis (ICD 575). Only the 1st reported diagnosis of either ICD category is included in the analyses. In the 1974 report, the ratio for current users to controls was 1:32. This association was not supported by the current ratio of 1:12. In this analyses, the ratio of current users to controls for women whose 1st reported diagnosis was cholecystitis was significantly raised. As this observation is difficult to interpret because cholecystitis and cholelithiasis have a common pathology and usually coexist, only total gallbladder disease is considered for the remainder of this report. The lack of an excess of total gallbladder disease was a surprise in view of earlier data and other studies relating to short-term use. When standardized for age, smoking, and parity, and for the effects of different dosage and type of hormone, the initial rise in incidence observed during the first 4 years of use was followed over the next 6 years by a steady decline to a rate below that in controls. Since any effects due to differences between brands of OCs used have been eliminated by standardization, prescribing changes during the course of the study to lower dose preparations cannot explain these findings.