A nurse is educating a patient who has been prescribed tamoxifen for breast cancer. Which instruction should the nurse prioritize to ensure early detection of serious adverse effects?

Rationale: A. Hot flashes are a common, expected side effect of tamoxifen and are usually not dangerous. Stopping the medication without consulting the provider could reduce the effectiveness of breast cancer treatment. B. Taking tamoxifen with food may help reduce minor gastrointestinal discomfort, but this is not the priority safety concern. Gastrointestinal upset is generally mild and not life-threatening. C. Tamoxifen increases the risk of endometrial cancer and thromboembolic events. Unusual vaginal bleeding, spotting, or discharge can be an early sign of endometrial cancer or other serious complications. Prompt reporting allows early evaluation and intervention, making this instruction a priority for patient safety. D. Grapefruit can interact with some medications metabolized by CYP3A4, but it is not a major concern with tamoxifen. While general dietary precautions can be discussed, early detection of serious adverse effects takes precedence.