# Diindolylmethane (DIM)

Source: https://onco.cc/technologies/diindolylmethane-dim/  
OnCo record `diindolylmethane-dim` (Technology). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

DIM is a broccoli-derived compound sold to 'balance oestrogen'. In a randomised trial in women taking tamoxifen for breast cancer, it lowered the blood level of endoxifen, the form of tamoxifen that does most of the work, so it should not be taken alongside tamoxifen without the oncologist's agreement.

## Summary

Diindolylmethane is the main metabolite of indole-3-carbinol. Memorial Sloan Kettering's About Herbs entry reports limited human data: daily DIM may affect the androgen receptor in castration-resistant prostate cancer, results in cervical abnormalities are mixed, and small studies show changes in oestrogen metabolism, including in women with a history of early breast cancer. In a randomised trial of women with oestrogen receptor-positive breast cancer taking tamoxifen, DIM increased the ratio of 2-hydroxyoestrone to 16-alpha-hydroxyoestrone, a biomarker change in the desired direction, but also significantly reduced serum endoxifen and other tamoxifen metabolites, without measured effects on breast density or sex hormone-binding globulin. MSK states that the effect on breast cancer risk is unknown and that more research is needed on tamoxifen efficacy when taken with DIM. Case reports include central serous chorioretinopathy after excessive intake, a drug rash with eosinophilia, an ischaemic stroke and a pulmonary embolism with deep vein thrombosis. Because of hormonal effects it should not be used in pregnancy, when planning pregnancy or breastfeeding, and MSK advises caution with the contraceptive pill and with drugs metabolised by CYP enzymes or transported by MDR1.

## Fields

- Kind: Technology
- Status: phase-2
- Last checked: 2026-11-04
- Also known as: DIM; 3,3'-diindolylmethane
- Tags: complementary; supportive-care; evidence:harm
- Principle: Alters cytochrome P450 activity and oestrogen metabolism; the same enzyme changes reduce conversion of tamoxifen into its most active metabolite.
- Strengths: Randomised data exist in women on tamoxifen, which makes the interaction measurable
- Limitations: Lowered endoxifen in women taking tamoxifen; Effect on cancer risk unknown; Case reports of thrombosis and stroke

## Sources

- MSK About Herbs: Diindolylmethane (page last updated 15 December 2023): https://www.mskcc.org/cancer-care/integrative-medicine/herbs/diindolylmethane

## Connected records

- technologies: [DHEA (dehydroepiandrosterone) supplements](https://onco.cc/technologies/dhea-supplements/), [Dietary supplements during cancer treatment: interactions and harms](https://onco.cc/technologies/dietary-supplements-treatment-interactions/), [Endocrine therapy (SERMs, AIs, SERDs)](https://onco.cc/technologies/endocrine-therapy/), [Evidence-based integrative oncology](https://onco.cc/technologies/integrative-oncology/), [Indole-3-carbinol (I3C)](https://onco.cc/technologies/indole-3-carbinol/)
- cancers: [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/), [Prostate cancer](https://onco.cc/cancers/prostate/)
- fronts: [Hormonal Therapy](https://onco.cc/fronts/hormonal/), [Prevention & Risk](https://onco.cc/fronts/prevention/), [Supportive Care & Survivorship](https://onco.cc/fronts/supportive-care/)
- drugs: [Tamoxifen](https://onco.cc/drugs/tamoxifen/)
- bottlenecks: [Toxicity and quality of life are undervalued](https://onco.cc/bottlenecks/b-toxicity-qol/)

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