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Prior studies suggest that histamines may modulate the development of colorectal neoplasia. To assess whether histamine receptor antagonist use was associated with adenoma formation. Patients ( n = 2366) were drawn from three adenoma chemoprevention trials. All underwent baseline colonoscopy with removal of adenoma(s) and were deemed free of remaining lesions; they were followed with surveillance colonoscopy. Medication use was assessed by questionnaire. Adjusted risk ratios for adenoma formation related to histamine receptor antagonist use (histamine H1 and H2 receptor, H1RA and H2RA) were determined using log linear models. In pooled analyses, H1RA exposure was not associated with subsequent adenoma risk (RR = 1.10; 95% CI 0.97–1.25) or multiple adenoma formation (RR = 0.85; 95% CI 0.67–1.07). H2RA use also was not associated with adenoma (RR = 0.90; 95% CI 0.77–1.06), or multiple adenoma (RR = 0.77; 95% CI 0.57–1.04) in the pooled analyses, but H2RA users in the first trial had a decreased risk of adenoma (RR = 0.70; 95% CI 0.48–1.03) and multiple adenoma (RR = 0.31; 95% CI 0.12–0.79). H2RA use was associated with reduced risk for adenoma in one trial, but not in the pooled analyses. Further study would be warranted before undertaking randomized trials of H2RAs for adenoma chemoprevention. [ABSTRACT FROM AUTHOR]