Male pattern hair loss is most common cause of hair loss in male where you lose hair from sides and top. This is mainly due to gene and hormone. You need maintenance therapy to maintain existing hair and other treatment for regrowth. Also you need to do some blood tests to find other causes of hair loss.  Minoxidil solution 5% in a dose of 1 ml twice daily will help for maintenance plus there are other treatment options like PRP and dermaroller.