According to the menscript health website, which specializes in hair loss treatments in the UK the treatment works.
The loss of male hair pattern also called androgenetic androgenetic Alopecia (AGA) is a noticeable, progressive loss of hair on the scalp in males who are genetically vulnerable. This gradual miniaturisation of hair follicles can be attributed to the shorter length of the anagen growth phase, and a decrease in the volume of the matrix of hair. This results in the gradual transformation in large terminal follicles into smaller follicles, which produce finer and shorter hairs. In follicles on the scalp that are susceptible to infection, dihydrotestosterone (DHT) binds to the androgen receptor as well as the hormone receptor complex in some way, which triggers genes that control the process of miniaturisation. In comparison to the occipital scalp the frontal scalp of males who have AGA is more enriched with DHT 5a-reductase type 2, type 2 along with androgen receptor.
Finasteride is a type 2 5-a-reductase inhibitor found to lower levels of DHT on both the scalp and serum. Clinical studies have demonstrated that finasteride can slow the progression of loss of hair and boosts hair growth in males with AGA that is predominantly frontal or vertex-based. A double-blind, placebo-controlled trial of patients suffering from AGA discovered Finasteride (1 mg/d) decreased the loss of hair and enhanced hair growth over a period of five years. Similar to a placebo-controlled study which was followed by a one-year open extension found the fact that finasteride (1 mg/d) reduced hair loss and accelerated hair expansion in the frontoparietal hair.
For more information , see the complete article on Finasteride for male hair loss