What is tamoxifen? How does it interact with other drugs?

Tangeretin

Effect: Possible Harmful Interaction

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

Soy Isoflavones

Effect: 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 growth, but high doses of isoflavones augment the effectiveness of
tamoxifen.

Bibliography

Liu, B., et al. “Low-Dose Dietary Phytoestrogen Abrogates Tamoxifen-Associated Mammary Tumor Prevention.” Cancer Research 65 (2005): 879-886.