Tamoxifen breast cancer medication side effects by Ray Sahelian, M.D.
March 6 2016


Tamoxifen was sold by AstraZeneca Plc under the name Nolvadex but is now marketed by several generic drug makers. It remains the only drug approved for use in preventing breast cancer in women who have not yet reached menopause. Questions have been raised on the benefit versus risk profile for the use of tamoxifen in women with low to moderate risk of breast cancer recurrence. See the link for natural options in prevention or treatment of breast cancer.

   Tamoxifen is a medication in pill form that interferes with the activity of estrogen (a hormone). Tamoxifen has been used for more than 20 years to treat patients with advanced breast cancer. It is used as adjuvant, or additional, therapy following primary treatment for early stage breast cancer. In women at very high risk of developing breast cancer, tamoxifen may reduce the chance of developing the disease. Tamoxifen continues to be studied for the prevention of breast cancer. It is also being studied in the treatment of several other types of cancer. It is important to note that tamoxifen is also used to treat men with breast cancer.


Is Tamoxifen that helpful?
Tamoxifen, the pill that prevents breast cancer in high-risk women, does not appear in the long run to save many lives. Women at the highest risk of breast cancer do appear to live longer if they take tamoxifen. But for women at the low end of the high-risk group, the sometimes serious side effects of tamoxifen outweigh the benefits. Tamoxifen can cause blood clots and uterine cancer. Melnikow and her colleagues calculated that tamoxifen can extend life expectancy only when a woman's five-year risk of developing breast cancer is 3 percent or higher. This is especially true for women who have not had a hysterectomy, and thus risk endometrial cancer from taking tamoxifen. Many women are in any case switching to a newer class of drugs known as aromatase inhibitors to treat breast cancer or to the osteoporosis drug raloxifene to prevent it. Raloxifene, made by Eli Lilly and Co. under the name Evista, has been shown to prevent breast cancer as well as tamoxifen does, without causing as many blood clots, cataracts or as many cases of uterine cancer. Researchers report that women with breast cancer who switched to Pfizer Inc.'s drug Aromasin after taking tamoxifen were 17 percent less likely to die. In women considered at high risk of breast cancer, usually meaning they have a close relative with breast cancer, have had several suspicious-looking lumps, or other conditions, tamoxifen reduced their risk of breast cancer by 49 percent. Cancer, 2006.

How does it work?
Tamoxifen is prescribed to treat early and advanced stages of breast cancer and prevent breast cancer recurrence. Tamoxifen blocks estrogen, which can help fuel the growth of tumors in some cases.


Tamoxifen side effects, safety
The most common tamoxifen side effects are hot flashes and other menopausal symptoms, vaginal dryness, nausea, low libido, and mood swings. Other tamoxifen side effects reported include headache and menstrual changes. Some women who take it to treat or prevent breast cancer report experiencing a mental fogginess while on the drug,  Journal of Neuroscience, 2013. There have been reports of increased risk for endometrial cancer after several years of use.


Tamoxifen is currently used for the treatment of both early and advanced estrogen receptor (ER) positive breast cancer in pre- and post-menopausal women. However, using tamoxifen routinely to inhibit endogenous or exogenous estrogen effects is difficult because of its potential side effects.


South Asian J Cancer. 2013. Tamoxifen-induced endometrial carcinoma after a lag of 14 years.

Tamoxifen Alternative

Aromasin, known generically as exemestane, and similar drugs inhibit the enzyme aromatase, which is needed to produce estrogen. The aromatase inhibitors are now being used just after breast cancer surgery instead of tamoxifen in many women to keep the disease from returning.


Can a patient take CoQ10, 50 - 100 mg. daily. The following: Had lumpectomy on Tamoxifen 20 mg. and 80 mg. Diavon. Can Co Q10 increase estrogen, progesterone level? Can CoQ 10 increase the reoccurance of breast cancer?
   A. I have not seen studies regarding the interaction of CoQ10 with tamoxifen or Diavon. I doubt CoQ10 has a major influence on estrogen or progesterone levels and I have seen no evidence yet that it increases the risk for breast cancer.


I would like to know if saw palmetto is safe to take in patients with a history of hormonal breast cancer currently being treated with Tamoxifen. It is one of 20 ingredients found in a hair vitamin. Would love to hear your opinion as this is a very controversial topic.
   A. I have no reason to believe it is not safe but I have not seen any studies that address the influence of saw palmetto on breast cancer in those being treated with tamoxifen.