The majority of testosterone in the body is bound to a
sex hormone protein in the liver that transports the
testosterone throughout the bloodstream, prevents its
metabolism and extends it half-life.  Once it becomes
unbound from this sex hormone protein, this now
can enter cells throughout the body.  In
the scalp, skin and prostate this testosterone is
converted into 5a-dihydrotesterone (DHT) by the
enzyme 5
a-reductase.  DHT is a 3-10x more powerful
androgen than testosterone.  Androgen is any
compound that controls the development and
maintenance of male characteristics by binding to
androgen receptors. The cause of most hair loss is
DHT because this form of testosterone binds with hair
follicles and causes them to shrink. Blood flow to the
hair follicles is choked off and eventually these follicles
lose the capacity to produce hair.  Finasteride
functions by acting as an inhibitor of  5
Therefore, it prevents the conversion of testosterone
into DHT resulting in a partial reversal of certain types
of male pattern baldness related to testosterone.  
Finasteride is taken as a once daily pill (1mg) with
results appearing after several months.  The benefits
of Finasteride for baldness (Brand name,Propecia)
end if the drugs is discontinued.   

An illustration of how Propecia works:
          Adverse Effects of Finasteride

Since the introduction of this drug by Merck there
have been concerns about its side effects and much
has been researched and written about this topic.
However, there is no doubt that Finasteride is
effective in treating an enlarged prostate and male
pattern baldness.  Merck conducted a four year
study or Proscar involving more than 3,000 patients.
It reported that:

  • It could be a danger to a male fetus in a woman
    impregnated by a man taking Proscar  

  • Sexual dysfunction, mainly impotence was reported at twice
    the rate of men taking Proscar as compared to the control

  • Merck reported that this sexual dysfunction was reversible if
    this medication was no longer taken  

Potential side effects listed for finasteride in addition
to impotence are abnormal ejaculation, decreased
ejaculatory volume, erectile dysfunction and
testicular pain.  Subsequent reports have found that
may contribute to depression, male breast cancer
and anxiety.  Although there are numerous potential
side effects noted, the percentage of men reporting
these problems would indicate that for the vast
majority of men, this drug does not cause any
significant problems. One positive finding has been
that men taking 5mg of Proscar for an enlarged
prostate have a significantly reduced incidence of
prostate cancer.