Guide
DIM (diindolylmethane) side effects
There's no large safety study establishing common side-effect rates for DIM in a general population. What exists instead is a small number of published case reports describing serious, rare reactions — a stroke, a systemic allergic reaction, and a retinal condition — alongside a pharmacokinetics study that wasn't designed to track side effects at all.
There's no large safety trial establishing how common side effects are for DIM in a general population. What exists instead is a small number of published case reports describing serious, rare reactions — a stroke, a whole-body allergic reaction, and a retinal condition — plus a pharmacokinetics study that tracked DIM in the body but wasn't designed to record side effects at all.
What we don't have
A 2021 study that gave 7 healthy adults about 90.6 mg of DIM a day for a week, tracking it in blood and urine, is the clearest general-population human data we found on DIM in the body — but it measured DIM and its metabolites, not adverse events, so it doesn't tell us how often people taking that dose felt anything unusual (PMID 34035125). Most other human trials that did track safety outcomes for DIM were run in specific hormone-related research populations, covered in DIM benefits: what the research does and doesn't show, and those results don't necessarily generalize to a healthy adult taking DIM for a different reason.
Rare, serious reactions in published case reports
Three individual case reports describe serious reactions attributed to DIM. A stroke case: a healthy 38-year-old woman had an ischemic stroke, discovered to be linked to an undiagnosed heart defect (a patent foramen ovale) in combination with DIM supplement use; the case authors present it as a reminder that supplement use is worth investigating as a rare contributing factor in an otherwise unexplained stroke in a young person, not proof that DIM alone caused it (PMID 36448494). A systemic allergic reaction: a case report titled to describe exactly this documents DRESS syndrome — a serious, whole-body drug hypersensitivity reaction involving rash, eosinophilia (a type of white blood cell increase), and systemic symptoms — attributed to a DIM supplement (PMID 26298826). A vision case: a woman developed a retinal condition (bilateral central serous chorioretinopathy) with headaches and blurred vision after two months of excessive, self-directed daily DIM use; her vision returned to normal within 8 weeks of stopping (PMID 25423641).
These are individually documented cases, not a measured rate across a study population — we can't say how common any of them is from three case reports. What they do establish is that serious reactions have been reported, in specific circumstances, and that stopping DIM was followed by improvement in at least one of them. A new or unusual symptom — a severe headache, vision changes, a widespread rash, or neurological symptoms — while taking DIM is worth stopping the supplement and seeing a doctor for, not something to wait out.
Milder effects some people report
We didn't find a controlled trial in a general population measuring the rate of milder effects — such as headache, nausea, or digestive upset — that people sometimes report anecdotally with DIM. Their absence from this page reflects a gap in general-population research, not a finding that they don't happen.
Questions people ask
Does DIM supplement make you sleepy?
We didn't find a study measuring drowsiness as an outcome for DIM. There's no research basis to say it does, or doesn't, in either direction.
Can DIM supplement cause dizziness?
No trial we reviewed measured dizziness specifically. If you experience dizziness after starting DIM, stop and check with a doctor, particularly if it's severe or persistent.
Does DIM supplement cause a skin reaction or allergic reaction?
A published case report documents a serious, whole-body allergic-type reaction (DRESS syndrome, involving rash and systemic symptoms) attributed to DIM. Any rash, especially one accompanied by fever or swelling, is a reason to stop the supplement and see a doctor right away.
Will DIM supplement side effects go away?
In the one case report describing a resolved reaction — a retinal condition with vision changes — symptoms improved within 2 weeks of stopping and fully resolved within 8 weeks. That's one documented case, not a general timeline; any concerning symptom should be evaluated by a doctor rather than waited out.
Related reading: who should not take DIM?, DIM and medications: what to check, and how much DIM should you take a day?
Sources
- 3,3'-Diindolylmethane Exhibits Significant Metabolism after Oral Dosing in Humans A 2021 pharmacokinetics study in 7 healthy adults taking about 90.6 mg of DIM a day (two capsules of an absorption-enhanced formulation) for a week found the body extensively metabolizes DIM into several other compounds detectable in plasma and urine — more processing than earlier studies had found, which reported only unchanged DIM.
- The Serious Side of Supplements: An Ischemic Stroke in a Healthy 38-year-old Female A published case report describes an ischemic stroke in an otherwise healthy 38-year-old woman with an undiagnosed heart defect (a patent foramen ovale) who was taking a DIM supplement; the authors present it as a reminder to consider supplement use as a rare contributing factor in unexplained stroke, not as proof that DIM alone caused it.
- Drug rash with eosinophilia and systemic symptoms caused by the dietary supplement diindolylmethane A published case report, titled to describe exactly this, documents a serious systemic allergic-type reaction (DRESS syndrome) attributed to a DIM supplement.
- Bilateral central serous chorioretinopathy associated with estrogen modulator diindolylmethane A published case report describes a woman who developed a serious retinal condition with headaches and blurred vision after two months of excessive daily DIM use; her vision returned to baseline within 8 weeks of stopping.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.