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Tamoxifen

Also indexed as: Nolvadex®

Tamoxifen is an antiestrogen drug primarily used to treat women with breast cancer or possibly to help prevent breast cancer in women at high risk. It is also used to treat mastalgia (painful breasts) and gynecomastia (abnormal breast enlargement in males).

Interactions with Dietary Supplements

Citrus flavonoids
Preliminary research in animals found that the citrus flavonoid tangeretin (found primarily in the peel of citrus fruits) interferes with the ability of tamoxifen to inhibit tumor growth.1 Although the evidence is far from conclusive, people taking tamoxifen should probably avoid citrus bioflavonoid supplements, as well as beverages and foods to which citrus peel oils have been added.

Gamma-linolenic acid
Gamma-linolenic acid (GLA), found in evening primrose and borage oils, may enhance the therapeutic effects of tamoxifen. A small group of breast cancer patients took 2.8 g of oral GLA per day in addition to tamoxifen, in a preliminary trial.2 Another group of breast cancer patients took tamoxifen alone. Those taking the GLA-tamoxifen combination appeared to have a better clinical response than did those taking tamoxifen alone. However, the results of this preliminary research are far from conclusive and need to be confirmed in a larger, more definitive trial.

Melatonin
In preliminary research, large amounts of melatonin were used successfully in combination with tamoxifen in a few people with breast cancer for whom tamoxifen had previously failed.3 The amounts used in this study should be taken only under the supervision of a doctor.

Tocotrienols
Tocotrienols are compounds similar to vitamin E that are found in palm oil. Test tube studies have shown that tocotrienols enhance the effects of tamoxifen.4 Controlled studies are needed to determine whether supplementing with tocotrienols might enhance the anticancer effects of tamoxifen.

Summary of Interactions for Tamoxifen

Depletion or interference None known
Adverse interaction Citrus flavonoids (tangeretin)
Side effect reduction/prevention None known
Supportive interaction Gamma linolenic acid (GLA)
Melatonin*
Tocotrienols*
Reduced drug absorption/bioavailability None known

For the convenience of the reader, the information in the summary is categorized as follows: “Depletion or interference” indicates the drug may deplete or interfere with the absorption or function of the supplement or herb. “Adverse interaction” indicates that the supplement or herb used together with the drug may result in undesirable effects. “Side effect reduction/prevention” indicates the supplement or herb may reduce the likelihood and/or severity of a potential side effect caused by the drug. “Supportive interaction” indicates the supplement or herb may support or aid the function of the drug. “Reduced drug absorption/bioavailability” indicates that the supplement or herb may decrease the absorption and/or activity of the drug in the body. An asterisk (*) next to an item in the summary indicates that the interaction is supported only by weak, fragmentary, and/or contradictory scientific evidence.

References:

1. Bracke ME, Depypere HT, Boterberg T, et al. Influence of tangeretin on tamoxifen’s therapeutic benefit in mammary cancer. J Natl Cancer Inst 1999;91:354–9.

2. Kenny FS, Pinder SE, Ellis IO, et al. Gamma linolenic acid with tamoxifen as primary therapy in breast cancer. Int J Cancer 2000;85:643–8.

3. Lissoni P, Barni S, Meregalli S, et al. Modulation of cancer endocrine therapy by melatonin: A phase II study of tamoxifen plus melatonin in metastatic breast cancer patients progression under tamoxifen alone. Br J Cancer 1995;71:854–6.

4. Guthrie N, Gapor A, Chambers AF, Carroll KK. Inhibition of proliferation of estrogen receptor-negative MDA-MB-435 and -positive MCF-7 human breast cancer cells by palm oil tocotrienols and tamoxifen, alone and in combination. J Nutr 1997;127:544S–8S.