If 1/2mg Finasteride is 80% Effective, Does that Mean 80% of the Side Effects?

If Finasteride (Proscar, Propecia, etc.) is 80% as effective at half the often prescribed 1mg dosage, it seems unlikely to me that reducing a patient’s dosage to 0.5mg would significantly reduce the likelihood or severity of the side-effects associated with the drug. In your practice, have you seen any evidence that suggests that reducing the dosage of Finasteride also reduces the potential for experiencing its side effects?

I have seen men who have had negative sexual side effects (decreased libido), who then took 1/2 dose (0.5mg) of finasteride and the side effects went away. I also have seen many of those with side effects, have them go away in a month or two without reducing the dose.