AbstractPurposeExperimental studies in rodents demonstrated the carcinogenic potential of phenolphthalein, the active ingredient in some laxatives, administered at doses similar to the dose that could be used by humans. Ovarian cancer was one of the cancers observed in these studies. We examined the association between epithelial ovarian cancer and use of phenolphthalein‐containing laxatives in a population‐based case‐control study.MethodsThe study includes 356 epithelial ovarian cancer cases (256 invasive, 100 borderline) and 424 controls. Cases were identified through a population‐based registry in Los Angeles County in 1992–1998, and controls were matched to cases by age, race/ethnicity and neighborhood. Data on laxative use (specific brands, frequency of use, usual dose) were obtained by structured in‐person interview.ResultsCompared to women who never used a laxative, ever use of a phenolphthalein‐containing laxative was not associated with an increased risk of invasive ovarian cancer (odds ratio (OR) 1.1, 95% confidence interval (CI) 0.75, 1.5) or of borderline ovarian cancer (OR 0.75, 95%CI 0.37, 1.5). Total days used, mean number of pills per day and cumulative dose were also unrelated to risk.ConclusionsThis study provides some assurance that phenolphthalein‐containing laxatives do not increase the risk of ovarian cancer in humans. These findings are of particular importance to those countries in which phenolphthalein is still used in over‐the‐counter medications. Published in 2003 John Wiley & Sons, Ltd.