The biggest side effect of propecia is sexual side effect. Number of people asked me about Sex drive and sex desire.
Sexual Drive and Sexual Desire are two different things.
Sexual desire is whether you WANT TO DO it. Sexual Drive is whether you CAN DO IT. So WANT TO DO is is your internal thought or your wish, which is not affected by Finasteride. Now sexual drive that is CAN DO IT is followed after WANT TO DO IT, which may affect by Finasteride. According to my experience, Finasteride can hamper your CAN DO IT. It does not hamper your WANT TO DO IT. So If you have a desire, the drive is possible. And drive may not be possible, if you take finasteride.
However It is my experience that as your body gets used to Propecia finasteride, sexual side effect slowly disappears in a couple of months.