If I use 1mg finasteride only 3 times a week. Would it be effective?

Currently you are taking 1 mg of finasteride 3 times a week.  The question I have is why are you only taking it 3 times a week.  The recommended dosage is 1 mg daily.  I have some patients who develop side effects from the full dosage and therefore we lowered their daily intake to minimize any side effects.  Now even though you are only taking 1 mg 3 times a week, there is some evidence that you will derive some benefit from this dosage.  

you should use 1 mg dose of finasteride routinelly every day .,If you miss the doses , efficacy of drug will decrease and you would not get max potential effect of it.

Reducing the dose to 1 mgs three times a week will still be effective, but slightly less that the same dose daily