The US Preventive Services Task Force does not recommend routine annual mammography screening for women aged 40-49 at average risk. Little research has been done to develop theory-based communication interventions to facilitate informed decision-making about reducing potentially low-value mammography screening. Evaluate the effects of theory-based persuasive messages on women's willingness to consider delaying screening mammography until age 50 or have mammograms biennially. We conducted a randomized controlled communication experiment online with a population-based sample of U.S. women aged 40-49 (N = 383) who screened to be at average risk for breast cancer. Women were randomly assigned to the following messaging summaries: annual mammography risks in 40s (Arm 1, n = 124), mammography risks plus family history-based genetic risk (Arm 2, n = 120), and mammography risks, genetic risk, and behavioral alternatives (Arm 3, n = 139). Willingness to delay screening or reduce screening frequency was assessed post-experiment by a set of 5-point Likert scale items. Women in Arm 3 reported significantly greater willingness to delay screening mammography until age 50 (mean = 0.23, SD = 1.26) compared with those in Arm 1 (mean = -0.17, SD = 1.20; p = .04). There were no significant arm differences in willingness to reduce screening frequency. Exposure to the communication messages significantly shifted women's breast cancer-related risk perceptions without increasing unwarranted cancer worry across all three arms. Providing women with screening information and options may help initiate challenging discussions with providers about potentially low-value screening.