Tamoxifen is a drug related to estrogen. It is called an agonist/antagonist, because it blocks the actions of estrogen and at the same time produces some estrogen-like actions. Tamoxifen is primarily used for the prevention and treatment of breast cancer [3].


Tangeretin

Possible Harmful Interaction

Tangeretin is a bioflavonoid found in citrus fruit and some citrus bioflavonoid [4] supplements. Animal studies suggest that high intake of tangeretin reduces the effectiveness of tamoxifen. 1 [5] For this reason, people using tamoxifen should avoid supplements containing tangeretin, and should also probably avoid excessive intake of citrus fruit.


Soy Isoflavones [6]

Mixed Interaction

Like tamoxifen, soy isoflavones have both estrogen-like and anti-estrogen actions. Test-tube and animal studies suggest that relatively low doses of soy isoflavones interfere with the ability of tamoxifen to inhibit breast cancer [3] growth, but high doses of isoflavones augment the effectiveness of tamoxifen. 1 [5]