Diindolylmethane or (DIM) is an extract derived from cruciferous vegetables like broccoli and a cabbage, so most people would assume that it’s safe. After all neither of those vegetables sound like something that would be likely to cause any notable harm, but since studies have begun to show that it can have an impact on hormone levels, there have been questions.
So Is DIM Safe?
The good news is that DIM supplements have been taken people under clinical conditions for years with no reports of serious adverse effects. However, it is essential to understand that DIM may interact with hormone levels and affect genes associated with cancer. 
Generally the initial studies which we’ll talk about shortly have shown it to be a positive modifier, but that doesn’t always mean things like this are consistent.
Safe Dosage of DIM
Generally speaking doses ranging from 108 to 900 mg have been used in several trials with no noted issues.
DIM Side Effects
It’s also worth noting that there are some common side effects of DIM supplements, which are:
- Darkening of urine
- An increase in bowel movements
Less common side are:
- Skin rash
Understanding DIM What Makes It Do Anything At All?
When we consume cruciferous vegetables, such as broccoli or cauliflower, our stomach acid breaks down a compound called indole-3-carbinol which then converts into Diindolylmethane (DIM).
This conversion is thought to occur due to the action of plant enzymes found in these vegetables. DIM has been found to influence the activity of estrogen in the body, playing a role in hormone balance. 
And whilst some estrogen in men is fine, excessive estrogen levels have been associated with health problems.
DIM is believed to have a direct effect on estrogen and its metabolism in the body. It has been shown to increase the production of "good" estrogen metabolites, such as 2-hydroxyestrone, while reducing the levels of "bad" estrogen metabolites like 16 alpha-hydroxyestrone. 
When we say bad in this case, we mean the types of molecules that break estrogen down into waste that can cause stressors on the body rather than harmless compounds.
Ultimately this means that it can be beneficial for women too as it doesn’t so much reduce metabolism of estrogen for them all together, but more how estrogen is broken down.
DIM and The Prostate
Prostate enlargement and prostate cancer are hormone-sensitive conditions there’s been a recent study that suggests DIM may play a role in inhibiting their development.
In a 12-month study involving men with high-grade prostatic intraepithelial neoplasia (PIN), a condition considered a precursor to prostate cancer, those given DIM supplements experienced significant improvements in prostate health and PIN. 
There’s also been a few animal and test tube studies that have shown similar results, but of course this is far from conclusive.
DIM and Women’s Health
There have been a couple of studies suggesting that DIM can reduce the risk of breast cancer, as it inhibits 16 alpha-hydroxyestrone, which we mentioned earlier. Two studies have been conducted on this, one which showed less cancer signs after one year and another study involving post-menopausal women with early-stage breast cancer found that DIM supplementation resulted in beneficial changes in estrogen levels. [5,6]
Although once again this is far from enough evidence to make any substantial conclusions.
What About Using DIM for Weight Loss?
There have been several supplements that claim DIM can help with weight loss due to it’s impact on estrogen levels, however, there have been no human studies to support these claims.
1 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3015182/
2 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4120774/
3 - https://pubchem.ncbi.nlm.nih.gov/compound/16alpha-Hydroxyestrone
4 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4197384/
5 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5571834/
6 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7566319/