There are thousands of products and treatments and lotions and potions that are said to help prevent hair loss but, to our knowledge, there are only two non-surgical treatments that have good scientific evidence that they can be effective.
These two medications are Minoxidil lotion (aka Rogaine, Regaine, Apogaine) which comes in 2% and 5% strengths and Finasteride tablets (aka Propecia, Proscar). Minoxidil and Finasteride work in different ways and can be used together, however they are only effective as long as you keep using them. Within 6-12 months of stopping them, you will lose the hair they helped you save and it will be as if you never used them. While Minoxidil and Finasteride can help slow down hair loss, at best you can see a moderate improvement in your hair. They cannot restore your hair the way hair transplantation can. Like all medications there are possible side effects, which should be discussed with your doctor.