I’m 25yrs old and have taken Propecia for 2 weeks before I noticed a severe drop in my libido. I have been off it for a week and it appears to be the same. How long does it take to run its course and exit your system? Is there any chance this is permanent like horror stories on the internet?

It leaves your blood stream in about a day or two. There is some tissue fixation which might last for up to a month (wild guess), but I would expect that everything should go back to normal well before a month. You should consult with the doctor who prescribed the medication for you.