I don't recall a limp boner being a side of propecia, they include impotence, less ejaculate and lower sex drive. All happend in less than 2% of the test subjects. Try Arginine to increase the blood flow 2g a day.
BTW who cares if you sex drive is lower chix just give you headaches anyway. We strive to get layed because it is a physical need. At my age I would rather not have a huge sex drive, chase women in bars, beet off to cable tv, catch diseases, waste money on stripers and p**rn- that sh*t gets old. As long as your equipment works when you do want to get it done. Thats like an alcoholic saying I am stopping my medication because I am loosing the desire to drink. A high sex drive is a curse- it always leads to some kind of trouble. So if Propecia can lower that good.
As Jims dad said in American Wedding "The longer your married the longer you can go without sex."