I just switched from Propecia to generic Proscar (cut into fourths). The pills I am cutting are extremely small, and thus difficult to cut! Always be sure consult your pharmacist about the size of generic Proscar before filling your script!
Consulting your pharmacist about the size of the pill is great advice. Let the pharmacist know that you’re going to be cutting the pill. Different generic drug makers could have different pill sizes for the 5mg finasteride. Fillers are often used to make the medication easier for the patient to handle or to make production easier.
Do you know the maker of the generic you got? There’s a partial list of generic finasteride names available here.