Letro is an extremely potent anti-estrogen which was originally developed to help treat breast cancer in women. It can also have benefits to bodybuilders who are very sensitive to estrogen related side effects, or who are in heavy bulking cycles and taking large amounts of aromatizing hormones such as testosterone. This product is extremely potent at blocking estrogen in the body, and studies typically show that a relatively low dose of Letro can eliminate up to 98% of the estrogen in the body.