Doctor recently prescribed Propecia for thinning hair (have a receding hairline and some light loss in the crowns). The treatment schedule is M, W, F, 1mg per day. My question is two-fold: a.) since the treatment schedule is less than 5mg every day of the week, is it still likely to help me regrow hair or at least help prevent existing hair to fall out? b.) is it likely to help decrease my chances of experiencing sexual dysfunction?

Those are all questions you should ask the doctor who presribed this medication. If he or she put you on this stuff without being able to advise on what the positive effects or possible side effects could be, it might be good to get a second opinion on whether this is right for you.