Many conditioners, shampoos, vitamins, and other products claim to help hair grow in some unspecified way. These are harmless but useless. To slow down hair loss, there are two basic options: 

Minoxidil (brand name: Rogaine): This topical application is over-the-counter, no prescription is required. It works best on the crown, less on the frontal region. Available as a 2% solution, Rogaine may grow a little hair, but is better at holding onto what's still there. There are few side effects with Rogaine. The main problem with this treatment is the need to keep applying it twice a day, and most men get tired of it after a while. In addition, Minoxidil works less well on the front of the head, which is where baldness bothers most men. This drug also comes in a higher strength, 5%, which may be a bit more effective. 

Finasteride (brand name: Propecia): This is a lower-dose version of a drug that shrinks prostates in middle-aged men. Propecia is by prescription and is taken once a day. Propecia does grow and thicken hair to some extent, but its main use is to keep hair that's still there. It's therefore best for men who still have enough hair to retain. One side effect is impotence, but this is no more common than it is in the general population, and is reversible when the drug is stopped. Taking Propecia once a day is easier that applying minoxidil, but the prospect of taking a pill daily for years doesn't sit well with some men. There's also the cost, about $60/month, not reimbursed by most health insurers. 

Minoxidil and Propecia are meant to be used indefinitely. Those who change their mind and stop are left where they would have been without them, but no worse. 

   

What other options do I have for hair loss?

Hairpieces, etc. 
Among the time-honored ways to add hair temporarily are hairpieces or hair weaving, in which a mesh is attached to your remaining hair and artificial or human hair of similar color and texture is woven with existing hair. Quality varies considerably with price; also, hairpieces and weaves stretch, oxidize, and loosen. 

Surgery 
Surgical approaches include various versions of hair transplantation (taking hair from the back and putting it near the front) or scalp reduction (cutting away bald areas and stitching the rest together). Transplant procedures have improved greatly in recent years. They can produce much more attractive and natural-looking results than older methods that sometimes left a "checkerboard" look. Many transplant patients now take Propecia to keep what they've transplanted. When considering a hair transplant, check the surgeon's credentials and experience carefully.