Tamoxifen (Nolvadex) is used to prevent and treat ER+ breast cancer. Unlike aromatase inhibitors, which block estrogen production, tamoxifen interferes with a tumor's ability to use estrogen. Alcohol can increase tamoxifen's side effects and reduce its effectiveness. Therefore, alcohol should be limited or avoided during tamoxifen treatment.

Drinking alcohol while taking tamoxifen

The effects of drinking alcohol while taking tamoxifen can vary greatly. Some women have reported that tamoxifen reduces alcohol tolerance, so that it takes less alcohol to result in intoxication and associated vomiting. Alcohol (whether wine, beer or hard liquor) can also increase tamoxifen side effects such as dizziness, drowsiness and menopausal symptoms. In some women, alcohol can also worsen nonalcoholic fatty liver disease (which can be caused by tamoxifen).

How alcohol interferes with tamoxifen treatment

Alcohol consumption has been found to be associated with increased risk of breast cancer, especially estrogen sensitive disease (ER+/PR+, ER+/PR-, or ER+/PR+/HER2+). Alcohol intake results in elevated levels of intracellular estrogen, which act through the estrogen receptor (ER) to promote breast cancer growth and proliferation. Consuming alcohol during tamoxifen treatment interferes with tamoxifen's abilty to block a tumor's use of estrogen.
One study reported that alcohol promoted breast cancer cell proliferation, increased growth factor signaling, and upregulated the transcription of certain ER target genes. The authors identified a number of alcohol-responsive genes, including those involved in programmed cell death as well as cell proliferation pathways. Alcohol was found to weaken the anti-proliferative effects of tamoxifen in ER+ breast cancer cells.
Please see our article on Foods to eat and avoid during tamoxifen treatment and the alcohol and tamoxifen tags for more information.