Tamoxifen is a medication that (we think) blocks the effects of estrogen on the breast. The exact mechanism by which it works is unknown.

However, we do know that the positive effects of taking Tamoxifen are well less than  many surgeons claim.

The Physicians’ Desk Reference (PDR) for prescription drugs reports that overall recurrence-free survival at 10 years of follow-up was 51.2 percent with Tamoxifen versus 44.7 percent without taking the drug.

That means taking Tamoxifen may provide a 6.5 percent (51.2 minus 44.7) reduction in recurrence of breast cancer.

Another way to look at these data is that there is a 92.5 percent (100 minus 7.5) chance that Tamoxifen will not help prevent recurrence.

The same data showed that if the lymph nodes were not affected, the survival benefit of taking Tamoxifen — compared to those with similar pathology — was 4.5 percent.

In other words, 95.5 percent of those who took Tamoxifen got no survival benefit at all.

It’s clear: Tamoxifen is not effective for the vast majority of women who take it. Still, we might be willing to accept these poor results if there were no serious adverse effects from Tamoxifen. Unfortunately, that’s not the case.

Serious side effects of taking Tamoxifen include:

• Increased risk of stroke

• Increased risk for developing uterine cancer

• Blood clots, including lung blood clots

• Liver problems

• High calcium levels in blood

• Early menopause