DIM (diindolylmethane)
Summary
DIM is a breakdown product of indole-3-carbinol from cruciferous vegetables. In trials it shifted estrogen metabolism and raised SHBG, but those are lab markers. The largest trial, 551 women with mildly abnormal cervical smears, found no effect on cytology or HPV. In women on tamoxifen, DIM lowered tamoxifen's active metabolites. Every oral trial here used BR-DIM, not plain DIM powder.
Key facts
- A compound derived from indole-3-carbinol, found in cruciferous vegetables[5]
- 551 women with low-grade cervical abnormalities: 150 mg/day for 6 months did not change cytology or HPV; the CIN2+ result was uncertain (RR 0.7, 0.4–1.2)[2]
- In a 12-month RCT, DIM lowered plasma endoxifen, 4-hydroxytamoxifen and N-desmethyltamoxifen in women taking tamoxifen[1]
- Raised the urinary 2/16α-hydroxyestrone ratio and SHBG; breast density did not change[1]
- Trials used microencapsulated BR-DIM; one capsule labeled 150 mg held 45.3 mg of DIM[5]
- 5 graded human outcomes on this page
- October 12, 2026
How it works
ProposedDIM is thought to act on estrogen metabolism, shifting it toward 2-hydroxyestrone (seen as a higher urinary 2/16α-hydroxyestrone ratio in trials), and to activate the aryl hydrocarbon receptor; a human metabolism study found hydroxylated DIM metabolites with receptor activity of their own. How these marker changes relate to health outcomes is unproven.[1][4][5]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
At a glance: strongest evidence per outcome
| Outcome | Grade | Effect | Strongest evidence | Rows |
|---|---|---|---|---|
| Cervical health | Grade C | No effect | RCT · n = 551 · 2012 | 3 rows |
| Breast / tamoxifen | Grade C | Mixed | RCT · n = 130 · 2017 | 1 row |
| Prostate | Grade D | Mixed | RCT · n = 45 · 2016 | 1 row |
Every graded row
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| Cervical cytology, CIN2+ and HPV in low-grade cervical abnormalities | No effect | Grade C | RCT · n = 551 · 2012 Women with newly found low-grade cervical cytological abnormalities (UK) Form: BioResponse DIM (BR-DIM) · Dose: 150 mg DIM once daily · Duration: 6 months CIN2 or worse in 9% on DIM vs 12% on placebo (RR 0.7, 95% CI 0.4–1.2); CIN3 or worse RR 0.9 (0.4–2.0). HPV persisted in 69% on DIM vs 61% on placebo (RR 1.1). The authors concluded DIM is unlikely to affect cytology or HPV, with uncertainty about CIN2+. | 22075942 (opens PubMed)Source [2] |
| Estrogen metabolism, breast density and tamoxifen metabolites in women taking tamoxifen | Mixed | Grade C | RCT · n = 130 · 2017 Women prescribed tamoxifen after breast cancer (USA); 98 completed (47 DIM, 51 placebo) Form: BioResponse DIM (BR-DIM, microencapsulated) · Dose: 150 mg twice daily (after a 75 mg twice-daily start in the first 10 participants) · Duration: 12 months The urinary 2/16α-hydroxyestrone ratio and SHBG rose versus placebo. Breast density on mammography and MRI did not change. Plasma endoxifen, 4-hydroxytamoxifen and N-desmethyltamoxifen fell versus placebo (P<0.001), and more women dropped below a proposed endoxifen threshold of 5.6 ng/mL. | 28560655 (opens PubMed)Source [1] |
| Regression of CIN I–II with DIM vaginal suppositories | Improved | Grade D | RCT · n = 78 · 2015 Women of reproductive age with CIN I–II (Russia) Form: DIM vaginal suppositories (not an oral supplement) · Dose: 100 or 200 mg/day intravaginally · Duration: 90–180 days Complete regression in 100% (200 mg), 90.5% (100 mg) and 61.1% (placebo). Adverse events were more frequent on DIM (40–42% vs 22%), none serious. | 26693258 (opens PubMed)Source [6] |
| Cervical lesions (CIN2–3) before planned excision | No effect | Grade D | Pilot RCT · n = 64 · 2010 Women with biopsy-proven CIN2 or CIN3 (USA) Form: BioResponse DIM (BR-DIM) · Dose: About 2 mg/kg/day · Duration: 12 weeks No statistically significant difference between DIM and placebo in any outcome; 2 people on DIM reported nausea. | 19939441 (opens PubMed)Source [3] |
| Prostate tissue DIM and biomarkers before prostatectomy | Mixed | Grade D | RCT · n = 45 · 2016 Men with organ-confined prostate cancer scheduled for surgery (USA) Form: BioResponse DIM (BR-DIM) · Dose: 100 or 200 mg twice daily · Duration: 21–28 days DIM was found in only 7 of 28 prostate tissue samples. The urinary 2/16-hydroxyestrone ratio changed versus placebo in the 400 mg/day group; PSA, testosterone and other markers did not change significantly. | 26313229 (opens PubMed)Source [4] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| Absorption-enhanced DIM (BR-DIM, microencapsulated) | Varies[1][2][3][4][5] | After a week of two 150 mg capsules nightly (45.3 mg DIM each), DIM plus hydroxylated metabolites and their conjugates appeared in plasma and urine.[5] | Darkened or discolored urine was common (40% in the tamoxifen trial; 31% vs 10% in the cervical trial); other adverse events were similar to placebo.[1][2] | All oral trials on this page (150–400 mg/day as labeled) |
| Plain DIM powder or capsules | Varies[1][2][3][4] | No trial cited here tested plain DIM; all oral trials used the BR-DIM formulation.[1][2][3][4] | No trial data for plain DIM.[1][2][3][4] | Not tested in the trials on this page |
| DIM vaginal suppository | Varies[6] | Applied vaginally, not swallowed.[6] | Adverse events were more frequent than with placebo (40–42% vs 22%), none serious.[6] | CIN I–II (one trial) |
Studied doses
Doses studied in human trials ranged from 150 mg/day (6 months, cervical abnormalities) to 300 mg/day (150 mg twice daily for 12 months alongside tamoxifen) and 200–400 mg/day for 3–4 weeks before prostate surgery, all using the BR-DIM formulation; one pilot used about 2 mg/kg/day for 12 weeks.[1][2][3][4]
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
Medicines
- TamoxifenRCTIn a 12-month RCT, DIM lowered plasma levels of tamoxifen's active metabolites (endoxifen, 4-hydroxytamoxifen, N-desmethyltamoxifen). Whether this weakens tamoxifen's effect is unknown.[1]
Who should be careful
- Taking tamoxifen
- DIM lowered active tamoxifen metabolites, including endoxifen, in a 12-month RCT; the clinical impact is unknown, so this combination needs the prescriber's input.[1]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
How to read the label
- Formulation weight vs DIM contentA human metabolism study measured 45.3 mg of DIM in a BR-DIM capsule labeled 150 mg. Trial papers are not always clear which they mean; the tamoxifen trial describes its dose both as "BR-DIM 150 mg" and as "150 mg DIM" twice daily.[5][1]
- Plain 400 mg productsEvery oral trial here used BR-DIM. A 400 mg serving of plain DIM has not been tested in these trials, so its blood levels and effects are unknown.[1][2][3][4]
- Urine colorDarkened urine is a frequent, reported effect in trials.[1][2]
Cost per studied dose, without the sales pitch
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Cost per studied dose
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Where to buy DIM (diindolylmethane)
Products from brands we partner with that contain DIM (diindolylmethane). Listing a product is not a claim that it works; check the amount per serving against the doses studied above, and the label for other ingredients.
- SupersmartPaid linkDIM (Diindolylmethane)4 capsules: 400 mg plain DIM; 30 servings. Trials used the BR-DIM formulation at 150–300 mg/day; plain DIM at 400 mg has not been tested in them.Shop at Supersmart (opens in new tab)Price and label checked 2026-10-11 on the brand’s site.
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Frequently asked questions
Does DIM interact with tamoxifen?
Yes. In a 12-month trial of women taking tamoxifen, DIM lowered blood levels of endoxifen and other active tamoxifen metabolites. Whether that reduces tamoxifen's benefit is unknown.[1]
Does DIM clear HPV or abnormal cervical cells?
The largest trial (551 women, 150 mg/day for 6 months) found no effect on cytology or HPV; a smaller pilot in CIN2–3 also found no difference from placebo.[2][3]
Does DIM balance estrogen?
It shifted estrogen metabolism toward 2-hydroxyestrone and raised SHBG in trials. These are lab markers; breast density did not change.[1][4]
Sources
- [1]A randomized, placebo-controlled trial of diindolylmethane for breast cancer biomarker modulation in patients taking tamoxifen.. Breast Cancer Res Treat, 2017. RCT
- [2]Effect of diindolylmethane supplementation on low-grade cervical cytological abnormalities: double-blind, randomised, controlled trial.. Br J Cancer, 2012. RCT
- [3]Oral diindolylmethane (DIM): pilot evaluation of a nonsurgical treatment for cervical dysplasia.. Gynecol Oncol, 2010. pilot-RCT
- [4]Phase Ib placebo-controlled, tissue biomarker trial of diindolylmethane (BR-DIMNG) in patients with prostate cancer who are undergoing prostatectomy.. Eur J Cancer Prev, 2016. RCT
- [5]3,3'-Diindolylmethane Exhibits Significant Metabolism after Oral Dosing in Humans.. Drug Metab Dispos, 2021. PK-study
- [6]Double-blind randomized placebo-controlled multicenter clinical trial (phase IIa) on diindolylmethane's efficacy and safety in the treatment of CIN: implications for cervical cancer prevention.. EPMA J, 2015. RCT
What changed
- First draft. Every PMID checked against NCBI E-utilities esummary (title and year taken from the record) and abstracts read for the cited rows.
- Adversarial review pass: every evidence row re-read against its PubMed abstract and the PMC full texts (PMC5571834 tamoxifen dose escalation and endoxifen threshold; PMC3251847 cervical adverse events and BioResponse supply). Flagged and disclosed: BR-DIM capsule weight vs DIM content (45.3 mg DIM per 150 mg capsule) and the tamoxifen paper describing its dose both ways. Tamoxifen interaction listed as an RCT-level interaction and an avoid entry. The vaginal suppository trial is marked as a different product. Retraction, expression-of-concern, erratum and withdrawn checks on all 6 PMIDs: none flagged.
- Independent adversarial review (PR #201): spot-checked cervical, tamoxifen, prostate, pilot, vaginal and metabolism rows against PubMed abstracts. Summary corrected: only the oral trials used BR-DIM (the vaginal suppository trial did not); summary trimmed. Tamoxifen interaction examples changed from a list to text to match the data schema (fixes a TypeScript error).