So lets create an imaginary scenario. You are a norwood 3 and with help from finasteride you back to a norwood 1, and then stop taking the meds. How long will it take to go back to the norwood 3? Does it happen instantly, or can it still take years?
iCurly is right. Generally you will lose all the gained hair within a year. There are exceptions to this though, like Ashton Kutcher who was almost a NW3 in his mid 20s and now at 40 is still NW1.5 after dropping dutasteride for almost half a year. It depends but its smart to go with the general census. NW3 to NW1 with just finasteride is crazy luck!