Final answer:
Tamoxifen, a drug investigated to reduce breast cancer risk, showed potential but also had adverse effects such as an increased risk of endometrial cancer and blood clots.
Step-by-step explanation:
Tamoxifen was investigated as a means to reduce breast cancer risk, and while the results were positive in this regard, the study also found some adverse effects.
The two principal side effects highlighted in research include an increased risk of endometrial cancer and the possibility of leading to blood clots. These adverse effects represent a significant consideration when evaluating the risk-benefit profile for the use of Tamoxifen in preventing breast cancer.