There's extensive posts about melatonin on the bodybuildingforum, it works better if you do a niacin flush (500mg) + melatonin (3mg) at night for a combination of AI and an immense GH boost from the niacin flush.
Studies show that women who take melatonin have a lower chance of getting breast cancer. " the activation of the estrogen receptor. It is thus considered to be a selective estrogen receptor modulator (SERM), that decreases both the expression of estrogen receptors alpha (ERα), and the ability of ERα to bind to DNA"
" Melatonin is also seen to be involved in the metabolism of estrogen, transforming estradiol into its inactive estrogen sulphate/sulfate form. This is another example of SEEM activity.
Melatonin is, as far as is known, the only molecule that has both SERM and SEEM properties. This double mechanism of anti-estrogenic effects, plus its invasiveness effects yields melatonin’s unique advantages for the treatment of hormone positive breast cancer."
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4979593/and this is waaay safer and cost-effective compared to Letro.