» Where are the studies that say progesterone can reverse hair loss?
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Here are some comments from a well-known authority in dermatology, Dr. Norman Orentreich, in his article: “Biology of Scalp Hair Growth”, Clinics in Plastic Surgery – Vol. 9, No. 2, 1982:
"Local Therapy
[…] Progesterone was found to be a natural and significant 5aR inhibitor when tested in vitro, in the human skin microsome system, a rich source of 5aR, and in human scalp hair follicles. When a solution of progesterone in alcohol was applied to the pubic skin of normal males, it caused an average decrease of 75.2 per cent in 5aR activity after 24 hours of treatment.
"Moreover, while less DHT is made, more dihydroprogesterone (DHP; 5a-pregnane-3,20dione) is made. DHP competes with the residual DHT for the cytosol-nuclear binding protein for a further reduction in the amount of DHT interacting with genetic material.
"Progesterone works in reducing DHT production locally by competing for the active site of 5aR and would need to be present at the active site continuously because of the reversible kinetics. Treatment lapses result in the resumption of DHT production from testosterone.
"Since progesterone only partially inhibits DHT production and since DHP only partially inhibits binding of residual DHT, local progesterone at best can only ameliorate androgenetic alopecia and not arrest it.
“Because more than 70 per cent of topically applied progesterone is metabolized in the skin to weak, nonandrogenic by-products, it can be used in women at the rate of 1 ml of a 2 per cent solution BID, whereas higher doses result in menstrual irregularities.”
Also, this would be a good place to mention what Sawaya and Shapiro said in their review article “Alopecia: Unapproved Treatments or Indications”, Clinics in Dermatology 2000;18:177-186: “Most therapeutic indications for progesterone are for ovarian disorders and contraception. Off-label uses have indicated variable effectiveness as a topical agent for treating AGA at 2% concentrations. We have not found that topical progesterone is of great value in the treatment of AGA”.
So it looks like topical progesterone might help a little, but it’s nothing to write home about.
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