For example the synthetic hormone PremPro that was commonly directed at menopausal women within the 1980 -90′s, is discovered to increase the incidence of cancer, cardiovascular disease, stroke and blood clots in the lungs (2002 World Health Initiative study, and 1996-2001 Million Women Study in the united kingdom).
This drug is really a combination of Premarin (synthetic estrogen based on pregnant horses) and Provera (synthetic progesterone called progestin) and it was approved by the FDA for treating hormone imbalances in women. When the news from the medical issues broke concerning this drug in 2002 many women abandoned this drug.
In the following year (2003) breast cancer rates in america declined an amazing 7% (Reported by MD Anderson Cancer Center at University of Texas). This is firm evidence that synthetic hormones are best avoided at all costs.