Most classifications of bioidentical hormones do not take into account manufacturing, source, or delivery method of the products, and so describe both non-FDA approved compounded products and FDA approved pharmaceuticals as bioidentical. The British Menopause Society has issued a consensus statement endorsing the distinction between "compounded" forms (cBHRT), described as unregulated, custom made by specialty pharmacies and subject to heavy marketing and "regulated" pharmaceutical grade forms (rBHRT), which undergo formal oversight by entities such as the FDA and form the basis of most clinical trials. Some practitioners recommending compounded bioidentical HRT also use salivary or serum hormonal testing to monitor response to therapy, a practice not endorsed by current clinical guidelines in the United States and Europe.Bioidentical hormones in pharmaceuticals may have very limited clinical data, with no randomized controlled prospective trials to date comparing them to their animal derived counterparts. Some pre-clinical data has suggested a decreased risk of venous thromboembolism, cardiovascular disease, and breast cancer. As of 2012, guidelines from the North American Menopause Society, the Endocrine Society, the International Menopause Society, and the European Menopause and Andropause Society endorsed the reduced risk of bioidentical pharmaceuticals for those with increased clotting risk. Compounding
Compounding for HRT is generally discouraged by the FDA and medical industry in the United States due to a lack of regulation and standardized dosing.
It has been suggested by some that the absence of significant effect in some of these studies could be due to selective prescription to overweight women who have higher baseline estrone, or to the very low progesterone serum levels after oral administration leading to a high tumor inactivation rate.Evaluating the response of breast tissue density to HRT using mammography appears to help assessing the degree of breast cancer risk associated with therapy; women with dense or mixed-dense breast tissue have a higher risk of developing breast cancer than those with low density tissue.Micronized progesterone does not appear to be associated with breast cancer risk when used for less than five years with limited data suggesting an increased risk when used for longer duration.A retrospective Cox proportional hazards analysis from Richard Neapolitan endorsed the reduced risk breast cancer with conjugated equine estrogen usage alone, but also suggested that conjugated equine estrogen with medroxyprogesterone acetate was associated with a risk reduction in breast cancer and that bioidentical hormone therapy was not associated with a statistically significant effect. There have been no prospective randomized clinical trials comparing the two routes of administration with regards to breast cancer.For women who previously have had breast cancer, it is recommended to first consider other options for menopausal effects, such as bisphosphonates or selective estrogen receptor modulators (SERMs) for osteoporosis, cholesterol-lowering agents and aspirin for cardiovascular disease, and vaginal estrogen for local symptoms. Observational studies of systemic HRT after breast cancer are generally reassuring.