Guide
DIM (diindolylmethane) and medications: what to check
A year-long human trial found adding DIM to tamoxifen reduced blood levels of tamoxifen's own active metabolites — a real, documented interaction worth knowing about. For most other medications, including hormonal birth control and antidepressants, no dedicated interaction trial exists, and animal research on liver-enzyme effects is a reason for caution rather than reassurance.
The clearest documented drug interaction for DIM is also the one it's studied most carefully: a year-long trial found that adding DIM to tamoxifen lowered blood levels of tamoxifen's own active metabolites. For nearly every other medication people ask about — hormonal birth control, antidepressants, thyroid medication, metformin — no dedicated interaction trial exists, and what's available instead is laboratory evidence of a plausible mechanism.
Tamoxifen: a documented interaction
A randomized, placebo-controlled trial followed 130 women who were prescribed tamoxifen, giving half of them 300 mg/day of DIM alongside their prescription for 12 months. DIM favorably shifted the estrogen-metabolite ratio researchers were tracking and raised a hormone-binding protein (SHBG) compared with placebo. But it also significantly reduced blood levels of tamoxifen's own active metabolites, including endoxifen, the metabolite considered most responsible for tamoxifen's effect. The study's own authors flagged this as a reason to determine whether the interaction could reduce tamoxifen's effectiveness — not as evidence that combining the two is beneficial (PMID 28560655). An earlier animal study found a related but distinct picture: DIM itself didn't change how rat livers metabolized tamoxifen, while indole-3-carbinol (DIM's precursor compound) did increase one tamoxifen metabolite, meaning the two compounds affect drug-metabolizing liver enzymes differently (PMID 15041081). If you take tamoxifen, this is not a case to guess about — tell your oncologist you're taking or considering DIM before you start.
Hormonal birth control, HRT, and TRT
No dedicated trial has tested DIM alongside hormonal contraceptives, hormone replacement therapy, or testosterone replacement therapy. Because DIM's proposed mechanism involves liver enzymes that also process estrogen (see what is DIM?), it's a reasonable question to raise with the doctor or clinic managing that treatment — but it's a question without a trial-backed answer either way, not a documented interaction like the tamoxifen finding above.
Liver-enzyme mechanisms, more broadly
Two animal studies in rats found DIM inhibits or alters the activity of several cytochrome P450 liver enzymes — the same family of enzymes responsible for metabolizing a wide range of prescription medications, not just estrogen (PMID 18486294, PMID 15041081). That's laboratory evidence of a plausible mechanism for a drug interaction, not a human trial confirming one for any specific medication beyond tamoxifen above. It's a reasonable basis for asking a doctor or pharmacist before combining DIM with any medication the liver processes, especially one with a narrow safety margin.
Antidepressants, thyroid medication, and other common prescriptions
We found no dedicated trial testing DIM against an SSRI or other antidepressant, a stimulant medication, metformin, or levothyroxine. That's an absence of evidence, not evidence of safety. Ask a doctor or pharmacist before combining DIM with any prescription medication, including these.
Questions people ask
Does DIM supplement interact with any medications?
The clearest documented interaction is with tamoxifen, where a year-long trial found DIM reduced blood levels of tamoxifen's active metabolites. For most other medications, no dedicated interaction trial exists — animal research suggests a plausible liver-enzyme mechanism, which is a reason to ask a doctor or pharmacist, not a tested answer.
Is DIM supplement a blood thinner?
No trial we reviewed measured DIM's effect on blood clotting directly. If you take a blood thinner, ask a doctor before adding any new supplement.
Can you take DIM supplement with birth control?
No dedicated trial has tested this combination. Given DIM's proposed effect on estrogen-metabolizing liver enzymes, ask the prescriber managing your birth control before combining them.
Can DIM supplement be taken with an SSRI, like Zoloft or Lexapro?
No dedicated trial has tested DIM combined with an SSRI. Ask a doctor or pharmacist before combining them.
Does DIM supplement affect thyroid medication?
No dedicated trial has tested DIM alongside thyroid medication. Ask a doctor or pharmacist before combining them, and take any thyroid medication as separately timed as your prescriber directs regardless.
Related reading: DIM side effects, who should not take DIM?, and DIM benefits: what the research does and doesn't show
Sources
- A randomized, placebo-controlled trial of diindolylmethane for breast cancer biomarker modulation in patients taking tamoxifen A year-long, placebo-controlled trial of 130 women taking tamoxifen found that adding 300 mg/day of DIM changed estrogen-metabolite ratios favorably but also reduced blood levels of tamoxifen's own active metabolites, including endoxifen — a finding the study authors flagged as a reason to determine whether it could reduce tamoxifen's effectiveness, not evidence that combining them is beneficial.
- Differences in the hepatic P450-dependent metabolism of estrogen and tamoxifen in response to treatment of rats with 3,3'-diindolylmethane and its parent compound indole-3-carbinol An animal (rat) study found DIM (unlike its parent compound indole-3-carbinol) did not change how the liver metabolized tamoxifen itself, but did reduce the activity of a liver enzyme (CYP3A) involved in metabolizing a range of other substances — a laboratory mechanism relevant to why drug interactions are plausible, not a human interaction trial for most medications.
- Inhibitory effects of a dietary phytochemical 3,3'-diindolylmethane on the phenobarbital-induced hepatic CYP mRNA expression and CYP-catalyzed reactions in female rats An animal (rat) study found DIM changed the activity of liver enzymes responsible for processing estrogen and, more broadly, other substances metabolized by those same enzymes — a laboratory mechanism, not a human safety trial.
*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.