Hair loss in males is so common, androgenic alopecia, you could call it the norm. It is usually genetic, although can occur from undue stress or trauma, and affects millions in the Western world. There's seemingly been no way to change that situation until recently, when a tablet is taken daily which contains finasteride.
You may see it called Propecia. The finasteride prevents or even reverses hair loss by inhibiting the conversion of testosterone into DHT, which causes hair follicles to shrink. There are possible side effects - best check these out with the pharmacist or doctor first - and the benefits won't be seen until you have been taking the tablet daily for a few months.