How does Propecia (Finasteride) work?

Introduction

Propecia is a prescription-only drug used to treat male pattern baldness. Unlike other drugs used for male pattern baldness, Propecia is a pill that is taken once daily. It works by preventing testosterone from being converted into DHT (dihydrotestosterone). In order to understand why inhibiting the production of DHT prevents hair loss and allows new hair to grow, one must first know why male pattern baldness occurs.

What Causes Male Pattern Baldness?

Male pattern baldness is a very common condition, affecting approximately 50 percent of men over age 50. Men who have male pattern baldness have higher levels of DHT in their scalp than men who do not have the condition. The DHT in the scalp causes individual hairs to become thinner and shorter. This process is known as follicular miniaturization.

Effects of Male Pattern Baldness

Over time, the affected hair turns into “peach fuzz”—short, fine hairs that are nearly invisible to the naked eye. As male pattern baldness progresses, hair loss may become very extensive, although usually the lower sides and back of the head are spared. 

How Propecia Works

When a man takes Propecia, testosterone in his body does not get converted into DHT. As a result, DHT levels in the scalp drop off and the hair stops thinning. In many cases, affected hair follicles enlarge and larger, thicker hairs grow in. Propecia works for about 90 percent of men who have male pattern baldness, although the results are far from perfect. A man who is quite bald cannot expect to regain a full head of hair from using this medication. Instead, most men find that their hair stops thinning and they regain a modest amount of hair.

Side Effects

The inhibition of DHT can cause effects other than ending hair loss and regrowth of lost hair. The most common side effects caused by Propecia are reduced sexual desire, erectile dysfunction and reduced ejaculate volume. Some men who take Propecia find that their skin, especially on their forehead, becomes oilier and they may develop acne as a result. However, each of these side effects occurs in fewer than 2 percent of men; most men who take Propecia do not experience any noticeable side effects.

Time Frame

Although DHT levels are reduced very quickly after starting treatment with Propecia, it takes time for the hair follicles to recover. Most men do not notice improvement for approximately three months after beginning treatment. Improvement continues for approximately one year, but the medication must be continued indefinitely to prevent hair loss from reoccurring. Men who stop taking Propecia usually lose the hair they regained while on the medication within one year.