Minoxidil solution influences directly the cell structure and cell activity of the hair follicle. Active relaxing the blood vessels, minoxidil accelerates blood flow to the hair follicles. The reason for this effect is still not fully known, but minoxidil as proved retards or stops hair loss and stimulates growth of normal, healthy follicles.

Minoxidil, prolonging the growth phase of hair, stimulates the follicles to start producing normal hair. Since it takes time for a significant number of hair to appear in the growth phase, the effect of minoxidil is noticeable only after 2-3 months after the start of use of the treatment. A year after the start of using it the number of hairs that are appear in the growth phase doesn’t increase and the effect is stabilized.

Unfortunately, we can not say that minoxidil solution will have equally acceptable result for all people. Sometimes minoxidil cause only the appearance of soft fine hair on the bald areas of the head, instead of a cosmetically acceptable pigmented hair growth. This result occurs when you try to regrow hair on the head which has been bald for a long time.
And yet, when it comes to female androgenetic alopecia or the early stages of male androgenetic alopecia, which is accompanied by thinning of hair on top, it is worth trying to save the hair, the chances of success, of course, are great.

Minoxidil solution helps women better than men, and helps balding people better than those ones who lost hair long time ago.

In clinical trials of minoxidil solution it was found that:
Minoxidil can be used to restore hair growth in areal and androgenetic alopecia.
Minoxidil treatment gives the first results in 2-3 months and causes the stabilization of hair growth in a year.

Hair growth is kept as long as the patient uses minoxidil. When you remove the treatment, hair loss starts again and goes back to the initial level.
The early stages of alopecia are treated much better than a long-term stage of complete baldness areas exposed to DHT.
Minoxidil (applied topically) is safe and does not cause adverse systemic effects, even during the prolonged usage. Skin reactions such as irritation and dryness of the skin of the scalp are rare and quickly pass.

From: http://www.minoxidil-plus.com/blog-and-news/15-how-does-minoxidil-work.html