I just heard back from the manufacturer of Propecia, Merck, concerning the question raised on April 29th (see: Propecia and Liver Disease). The question related to a person with a liver disease called Primary Scholerosing Cholangitis (PSC) and the safety issues with using Propecia.
A detailed three page answer was forwarded to me (with quotes from many scientific publications), so I will summarize it as simply as I can. The drug experience comes from Merck’s experience with Proscar (5mgs of Finasteride) and Propecia (1mg of Finasteride). A liver adverse effect has not been listed in the clinical trials of the drug for hair loss treatment. The drug itself is broken down by the liver, so decreased liver function will directly impact the rate at which the drug is metabolized by the liver and will keep serum levels higher in people known to have decreased liver function. In other words, the ability of the liver to clear this drug from the body may cause the serum levels to be higher than on someone without liver disease. There has been no study performed on the effects of hepatic insufficiency for Finasteride pharmacokinetics. Also, a search of the medical literature did show a rise in liver enzymes in one of 14 subjects studied in healthy volunteers (Shimazaki and Nose). One case of hepatitis induced by Finasteride was reported in a patient with many organ problems including a high alcohol intake. The inability to find another cause for the hepatitis on this patient led the doctors to believe that this drug may have been the cause for the liver disease on this one patient. When the drug Finasteride has been used with Flutamide, there was some impact possibly inducing liver disease.
In conclusion, I would strongly suggest that if you have known liver disease, that you use this drug with caution. Follow the use of the drug as prescribed in the literature and have a doctor follow your liver function tests periodically with the use of this medication. Liver disease in healthy people has not been reported (based upon the Merck communication with me). I would not consider liver disease as a significant risk in the typical patient’s routine use. But as a caution, every medication that anyone takes has potential risks associated with it. Even vitamins and Aspirin have their problems, yet we seem to continue to use them as well. The challenge is to balance reasonable risks against the alternative hair loss that might be slowed, stopped or reversed on this medication.