Today the internet is ablaze with news of a new treatment for baldness. A patient with Alopecia Areata, which is an autoimmune disease which causes the body to attack its own hair follicles causing them to fall out, was treated with a medication used to treat Rheumatoid Arthritis. After a number of months the patient grew back all the hair on his scalp (which he had previously lost because of the alopecia areata). There are many issues to be worked out beginning with the fact that this medication ingested orally can cause a large number of harmful side effects to the body so using it widespread to treat this form of hair loss may be considered dangerous. Also, alopecia areata work by a different mechanism to make hair fall out, so this medication probably would not be effective in typical genetic hair loss which is the most common form of hair loss.
Regardless, this is an exciting development in the treatment of alopecia areata and I would imagine that a topical formulation of this medication could hold significant promise for safe treatment of hair loss secondary to this disease.
I have included a link to the CNN article describing the findings in the original study.