The hormone 5-alpha dihydrotestosterone (DHT) is a metabolite of the "male" hormone testosterone. It is associated with two conditions common to men: benign prostate hypertrophy (BPH) and male pattern hair loss (MPHL). (See About Hair Loss for more information on male pattern hair loss).
Both conditions have been successfully treated medically with a drug that lowers the level of DHT available to prostate tissue and hair follicles. The drug is called a 5-alpha reductase inhibitor-a drug that inhibits the action of the enzyme 5-alpha reductase that converts testosterone into DHT.
One such drug, finasteride, has been in use, with U.S. Food and Drug Administration (FDA) approval, for several years. Under the brand names Propecia® it is used for treatment of MPHL, and under the brand name PROSCAR® for treatment of BPH. The dosages of finasteride are different in Propecia® and PROSCAR®, and each should be used for its specific indication for treatment of BPH or MPHL. (See Medical Hair Restoration for more information on finasteride).
Finasteride is identified as a 5-alpha reductase (type 2) inhibitor. This means that it inhibits the action of 5-alpha reductase (type 2), one of the two forms of the enzyme.
Dutasteride, a more recently developed drug, inhibits the action of both forms of the enzyme: type 1 5-alpha reductase and type 2 5-alpha reductase.
Dutasteride is currently approved by the FDA for use in the medical treatment of BPH under the brand name Avodart®.
While dutasteride has been used in other countries for treatment of MPHL, it has not yet received FDA approval for that use in the United States. Clinical trials of dutasteride as a treatment for MPHL are currently underway in the U.S., and investigators have reported successful outcomes (Olsen EA et al. Journal of the American Academy of Dermatology. 2006; Vol. 55, Pages 1014-1023).
The study reported by Olsen et al found that the inhibition of both type 1 and type 2 5-alpha reductase by dutasteride increased the effectiveness of the drug in treatment of MPHL.The most effective dose for treating MPHL was several times higher than the dose in Avodart® used to treat BPH.
In the skin, 5-alpha reductase (type 2) is the dominant form of the enzyme found in hair follicles, whereas 5-alpha reductase (type 1) is the predominant form in oil and sweat glands. The role of 5-alpha reductase (type 1) in MPHL-if any-is unknown.
The role of 5-alpha reductase (type 2) in MPHL has been well established by (1) studies showing that men with a congenital deficiency of 5-alpha reductase (type 2) do not experience MPHL, and (2) studies and clinical experience showing that finasteride, a 5-alpha (type 2) reductase inhibitor, has varying degrees of success in halting hair loss and restoring hair growth in men with MPHL.
[NOTE: 5-alpha reductase inhibiting drugs are not used to treat pattern hair loss in women who are, or may become, pregnant, due to possible effects of the drug on sexual development of a male fetus. Finasteride is taken orally, in pill form; minoxidil (Rogaine®), the other FDA-approved drug for hair restoration, is applied topically, and may be safely used by both men and women].
5-alpha Dihydrotestosterone (DHT) in BPH and MPHL Benign Prostate Hypertrophy (BPH)
The best understood cause of BPH is advancing age; enlargement of the prostate is common as men grow older. Prostate enlargement (hypertrophy) can have a hormonal basis, as prostate development and growth are influenced by 5-alpha dihydrotestosterone metabolized from testosterone by the action of the 5-alpha reductase enzyme. DHT is involved in growth of prostate tissue from childhood to old age.
The role of 5-alpha reductase (type 2) and 5-alpha dihydrotestosterone (DHT) on prostate enlargement is indicated by (1) studies showing that men with congenitally low levels of DHT do not experience prostate enlargement as they age, and (2) studies and clinical experience showing that treatment with a 5-alpha reductase inhibitor (PROSCAR® or Avodart®) lowers the level of DHT in prostate tissue and inhibits prostate enlargement in some but not all men so treated.
Male Pattern Hair Loss (MPHL)
The presence of increased levels of 5-alpha reductase (type 2) and 5-alpha dihydrotestosterone in hair follicles is associated with MPHL. In men, MPHL produces common patterns of hair loss ranging from recession at the temples to baldness over much of the scalp (See About Hair Loss).
Pattern hair loss associated with increased levels of 5-alpha DHT also can occur in women, but hair loss pattern are more diffuse than those common in men.
The "balding" associated with increased levels of 5-alpha DHT in hair follicles is due to the effect of DHT on the cycle by which scalp hair grows; in the presence of increased levels of 5-alpha DHT in hair follicles, the natural hair cycle is interrupted and newly produced hairs are miniaturized rather than achieving full growth.
The Future of Medical Treatment of MPHL
The continued development of 5-alpha reductase inhibiting drugs builds on the success of these drugs in treating MPHL. Availability of such drugs adds to the array of treatments for hair loss that can be offered to patients by physician hair restoration specialists, if examination and diagnosis confirms that treatment with such a drug is indicated.
[NOTE: Physicians may use a drug "off label" if such use would be of substantial benefit to the patient. "Off label" is a shorthand term for using a drug for a use not approved by the FDA (or similar regulatory agency in countries other than the U.S.). While dutasteride has not been FDA-approved for use in treating MPHL, it could be used "off label" for this purpose, but only with caution and after complete examination and diagnosis by an experienced physician hair restoration specialist. "Off label" use requires full knowledge and understanding of possible complications and side effects in an individual patient].