Sage Advice Blog

Curcumin and Tamoxifen: Concern for Interaction?

April 9, 2019

Alex Speers ND, MS


When recommending a supplement to a patient on drug therapy for cancer, we always have to consider the potential for an herb/drug interaction. One way in which herbs can interact with drugs is by altering the enzymes involved in that drug’s metabolism. Take, for instance, the drug Tamoxifen, which is given to patients with estrogen receptor-positive breast cancer. Tamoxifen is commonly taken for several years after a patient has completed surgery, radiation, and/or chemotherapy and its purpose is to reduce the risk of breast cancer coming back. One way in which Tamoxifen reduces this risk is by binding to estrogen receptors on breast cancer cells, preventing our body’s own estrogen from binding to those same receptors and stimulating cancer growth.


What is interesting however, is that Tamoxifen on its own has what is described as a “low affinity” for estrogen receptors. In other words, Tamoxifen isn’t that attracted to estrogen receptors. So how does it work? Well, when Tamoxifen enters our body, it is metabolized in our liver by two enzymes, called CYP2D6 and CYP3A4. These enzymes break Tamoxifen down into its active metabolites, which have a 30 to 100 times greater affinity for estrogen receptors. The active metabolites LOVE estrogen receptors and cannot help but strongly bind to them.


Now consider what might happen if an herb or dietary supplement inhibited one of these enzymes? In that case, Tamoxifen wouldn’t be broken down into its active metabolites as easily, leading to higher levels of Tamoxifen, which as we just mentioned, isn’t all that interested in binding to estrogen receptors. This could lead to a patient having sub-therapeutic levels of Tamoxifen’s active metabolites, potentially increasing the patient’s risk for a breast cancer recurrence.


All of this leads to a recent study published in the journal Cancers, where researchers investigated the potential effect of curcumin on the metabolism of Tamoxifen. Seventeen women taking daily Tamoxifen were given either curcumin alone (group A) or curcumin with black pepper (group B) in relatively high doses (3.6 grams of curcumin per day). After 28 days, the patients were switched to the other group.


What the researchers found was that taking curcumin alongside Tamoxifen significantly reduced the systemic exposure of Tamoxifen’s primary active metabolite endoxifen, meaning there was less endoxifen available to bind to estrogen receptors. This effect was much greater when curcumin was combined with black pepper, which increases curcumin’s absorption into the bloodstream. The researchers suggested that their findings were at least partially a result of curcumin’s ability to inhibit the enzyme CYP2D6, which as we discussed earlier would prevent the metabolism of Tamoxifen into its active metabolites.


It is important to note that while these findings were statistically significant, there is uncertainty regarding their clinical significance. In other words, would this combination really increase a patient’s risk of breast cancer coming back? We still don’t know that but given these findings, a conservative approach would be to avoid high-dose curcumin supplementation in patients with Tamoxifen, especially highly absorbable forms of curcumin. On the other hand, dietary turmeric, the plant from which curcumin is derived, is likely not a significant issue considering it is poorly absorbed and would result in much lower levels of curcumin in the blood. In conclusion, this study is another good reminder that patients with cancer should not begin taking supplements without first consulting a health practitioner who has significant experience combining supplements with anti-cancer drugs.


Reference: Hussaarts KGAM, Hurkmans DP, Oomen-de Hoop E, et al. Impact of curcumin (with or without piperine) on the pharmacokinetics of tamoxifen. Cancers (Basel). 2019;11(3). Pii: E403.


DISCLAIMER: These statements have not been evaluated by the Food and Drug Administration. There are no financial ties to any supplement companies, pharmaceutical companies, or to any of the products mentioned in this post. This post is not meant to treat, cure, prevent, or diagnose conditions or diseases and is meant for educational purposes. As always, please consult your doctor before trying any new treatments or supplements.

Return to Sage Advice Blog Main Page