How Herbal and Dietary Supplements Affect Oncologic Drugs

Reading time: 5 minutes

Susan Egbert

Statistics show that about 80 percent of the world’s population consume herbal/dietary supplements without specific recommendations to take them1, with some cancer patients using herbal/dietary supplements to alleviate their symptoms (e.g. pain, nausea, etc),2,3,4,5.  Generally, patients consider herbal/dietary supplements “safe” since they are “natural,” however, herb-drug interactions (HDI) (e.g. St. John’s wort and docetaxel) have been reported in 8% of patients taking one or two herbal products while on oral chemotherapy6.  Despite the increasing use of herbal/dietary supplements, there is not a significant amount of research trying to understand how these products can affect oncology regimens specifically. Some interactions that could be harmful include increase of drug levels in the blood which can cause patients to be at a higher dose than needed or drugs not being able to perform correctly because the herb is prohibiting the drug from reaching where it’s supposed to be.This article will not only dive into what has been done to understand herb-drug interactions in the world of oncology but also to emphasize how much is missing.

In a study done by Prely et al (2022), four online drug interaction databases (Thériaque®,®, Hédrine, and Memorial Sloan Kettering Cancer Center (MSKCC) database) were evaluated to assess their accuracy. These databases contain previously published studies of drug interactions, detailing the interactions and their effects.  In studies evaluated from 2017 to 2019, at least one interaction was found for 267 patients: 263 with drug-drug interaction (DDI-where drugs interact with each other), 68 with HDI (where any herbal compounds interact with drugs), and 64 with both7.  Hédrine® identified 36 high-risk HDI, and 10 weak risk interactions7. For HDI, 83 pharmaceutical interventions (any changes made to drugs because of another agent) that were performed in 60 patients: 75 led to herb discontinuation, 3 to therapeutic monitoring, 3 to pharmaceutical advice and 1 to drug intake optimization (making changes to the dosage of the drug in order to get the most beneficial effect from it). This analysis suggests care is needed when mixing herbal products with prescription medications.  Patients should mention every supplement and herbal product being used to their prescriber so that the prescriber can understand the full picture.

Gougis et al. 2021 also brought emphasis to understanding HDI in their review paper. Table 1 summarizes the herbal products and studies they discuss along with the conclusions. Although the use of some herbal products such as grapefruit and St John’s Wort has been well known to affect cancer treatment, it is noteworthy that other interactions were found. This included the combination of curcumin+piperine which modified the active metabolite of tamoxifen (a commonly used breast cancer drug).

Herbal productAnticancer DrugNumber of patientsConclusion
cannabisirinotecan17no significant modification of drug concentration
docetaxel14no significant modification of drug concentration
curcumin alonetamoxifen16drug concentration decrease 
curcumin+piperintamoxifen16drug concentration decreased by 12.4%
everolimus1 (x2)Concentration of drug decreased between 2 and 3 folds
echinaceadocetaxel10no significant modification of drug concentration
garlicdocetaxel10no significant modification of drug concentration
grapefruitdocetaxel1drug concentration increased by 2.6 fold 
Oral etoposide6drug concentration decreased by 26%
ibrutinib8drug concentration of ibrutinib increased by 2.1 fold
sunitinib8drug concentration increased by 11%
imatinib4no significant modification for drug concentration
Milk thistleirinotecan6no significant modification of drug concentration
St John’s wortirinotecan5drug concentration decreased by 42%
docetaxel10drug concentration decreased by 11% 
imatinib10drug concentration decreased by 32%
imatinib12drug concentration decreased by 30%
soytamoxifen136 vs. 154controlsno significant modification of drug concentration
Table 1. Adapted from Table 2 from Gougis et al 2021.

There is a need for more herbal drug interaction studies so that we can fully comprehend the interactions amongst them, which will also take us a step further in understanding any potential use as treatment for cancer patients. Limitations of current reviews/studies is the small sample sizes and the lack of diversity in the patients that were selected to undergo analysis.  Although there is more data appearing for non-Caucasian individuals, the majority of the clinical trials and studies still mostly have Caucasian patients that are participating in the study.  People with different ethnic backgrounds, age groups or comorbidities may have varying rates of metabolizing drugs and therefore need different therapies. 

Edited by Maha Said


  1. Clement YN, Williams AF, Khan K, Bernard T, Bhola S, Fortuné M, et al. A gap between acceptance and knowledge of herbal remedies by physicians: the need for educational intervention. BMC Complement Altern Med. 2005 Nov 18;5:20. Pmid:16297236
  2. Bahall M (2017) Prevalence, patterns, and perceived value of complementary and alternative medicine among cancer patients: a cross-sectional, descriptive study. BMC Complement Altern Med.
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  7. Prely, H., Herledan, C., Caffin, A. G., Baudouin, A., Larbre, V., Maire, M., … & Rioufol, C. (2022). Real-life drug–drug and herb–drug interactions in outpatients taking oral anticancer drugs: comparison with databases. Journal of Cancer Research and Clinical Oncology, 148(3), 707-718.
  8. Gougis P, Hilmi M, Geraud A, Mir O, Funck-Brentano C. Potential cytochrome P450-mediated pharmacokinetic interactions between herbs, food, and dietary supplements and cancer treatments. Crit Rev Oncol Hematol. 2021;166:103342. oi:10.1016/j.critrevonc.2021.103342

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