potential for a range of adverse effects in breasts, skin, eyes, cardiovascular, gastrointestinal, genitourinary or central nervous systems. Progesterone Progesterone can cause the emergence (or significant worsening) of abdominal pain, constipation, yeast infections, breast cancer, cystitis, acne, conjunctivitis, thrombotic disorders resulting in pulmonary embolus, strokes or heart attacks, epilepsy, migraine, asthma, and cardiac or renal dysfunction. Psychiatric reactions can include emotional instability, depression, aggression, decreased libido, and drowsiness. Adverse effects can also occur in the urinary, central or peripheral nervous, or musculoskeletal systems. A review of clinical trials studying bioidentical progesterone use found that it was ineffective in managing vasomotor symptoms of menopause, but had mild and self-limiting side effects. Administration Hormones can be administered in a variety of ways, including percutaneous skin and vaginal creams, oral pills, topical gels, vaginal rings and tablets, and transdermal patches. Although all preparations of a given type of estrogen may be molecularly identical before their introduction into the human body, estrogens administered orally are modified by the liver before entering the bloodstream and most of it is converted to estrone; estrogen bypassing the digestive tract and liver via the skin is not converted to a new form before entering the bloodstream. Creams and gels applied to the skin also enter the blood directly and without modification but absorption of the gels, creams, and patches can vary from application to application, depending on the temperature and condition of the skin. Criticisms Advocates for BHT have claimed that commonly compounded BHT preparations are not commercially available, but there are many FDA-approved hormone preparations containing bioidentical molecules available both as proprietary or generic brands. The exception is estriol, used in the compounded bioidentical preparations Triest and Biest—in 2008, the FDA banned estriol until a New Drug Application was completed; these preparations are not approved by the FDA or Health Canada. Some advocates of compounding have also claimed that customized compounding provides customized results, but the claim is weak since compounding is aimed at producing a single hormone profile with absolute blood or saliva levels—which has not been demonstrated to be better than CHRT—and does not consider the rate at which individuals will differ in the activity, metabolism and excretion of the hormones. There have been no clinical trials directly comparing the effectiveness or efficacy of bioidentical versus non-bioidentical compounds. A 2010 article published in The Medical Letter on Drugs and Therapeutics concluded that "[t]here is no