Topical finasteride reduces DHT in the scalp but does not have a beneficial effect on male pattern baldness, according to research on the topic. But then again, Merck did file a patent application for topical Propecia.
Here are some references:
1. Rushton DH, Norris MJ, Ramsay ID. Topical 0.05% finasteride significantly reduces serum DHT concentrations, but had no effect in preventing the expression of genetic hair loss in men. In: Van Neste D, Randall V, eds. Hair Research for the Next Millenium. Amsterdam: Elsevier, 1996: 359-62.
2. Townsend and Marlowe Ann. Relative Safety and Efficacy of Finasteride for Treatment of Hirsutism. Pharmacother. 2004; 38: 1070-1073.
3. Price TM, Allen S, Pegram GV. 2000. Lack of effect of topical finasteride suggests an endocrine role for dihydrotestosterone. Fertil Steril 74:414-415.
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