Finasteride takes 3 to 4 months to show any benefit. It can take up to a year to see the maximum results. Also, when you first start taking finasteride, it may even cause more shedding of fine hairs. Do not be concerned. This is expected. Also, some men do not respond to the medication and this can be as high as 1 out of every 10 men.
As long as you do not experience side effects, it is best to continue medication for one full year before deciding on whether the medication is doing all it can for you.