In mice with breast tumors that respond to estrogen, eating sesame seeds seems to block how well the breast cancer drug tamoxifen works, making tumors grow more than they do with the drug alone.

What we've found so far is that, in mice with estrogen-responsive breast tumors, eating sesame seeds may interfere with how well tamoxifen works. The evidence we’ve reviewed leans toward the idea that sesame seeds could reduce the drug’s effectiveness, leading to greater tumor growth compared to tamoxifen treatment alone [1]. Our analysis of the available research shows that in animal studies, sesame seed consumption was linked to a diminished response to tamoxifen [1]. Specifically, in mice, the addition of sesame seeds to the diet appeared to block some of the anti-tumor effects of the drug. This suggests that certain compounds in sesame seeds might interact with the way tamoxifen acts in the body, though exactly how this happens is not detailed in the evidence we have. We only reviewed one claim, supported by 9.0 studies, with no studies refuting it [1]. While this number suggests a pattern in the research, we don’t have enough context to know the quality, design, or consistency of those studies. Also, all findings are based on mice, not humans, so we can’t assume the same effects would happen in people. Our current analysis does not allow us to say this is definitely the case, nor can we explain the mechanism or determine risk levels. We also don’t know if other seeds or foods might have similar effects. Practical takeaway: If you’re undergoing tamoxifen treatment, it might be worth discussing sesame seed intake with your healthcare provider—especially if you eat large amounts—since early evidence in mice suggests a possible interaction.