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Why
doesn't propecia always work
Propecia does not always work for everyone with androgenetic alopecia.
There may be several reasons for this.
Propecia is a type II 5 alpha reductase inhibitor. That means it
blocks about 70% of the 5 alpha reductase activity in the body.
However, it has no effect on type I 5 alpha reductase which accounts
for a bout 30% of reductase enzyme activity in the body. So even
with propecia use there is always some conversion of dihydrotestosterone
(DHT) from testosterone. This limited DHT supply may be enough to
maintian androgenetic alopecia in some people.
It is well known that drugs such as Propecia are less effective
for people who have had pattern baldness for many years. This is
due to hair follicle destruction. In the early stage of pattern
baldness hair follicles become miniaturized but still produce small
vellus hairs. These hair follicles could still potentially be reactivated
to produce full terminal hair again. However, after several years
of miniaturization, hair follicles become so weak that they stop
growing altogether. These follicles are entirely destroyed. Once
destruction occurs it is impossible to stimulate these follicles
back into growth no matter how powerful the drug.
There are probably different types of pattern baldness where one
contributing factor important in promoting hair loss in one person
is different from the factor promoting hair loss in another person.
For example, DHT may be a big promoter of hair loss, but for another
person it may have a lesser role. Or perhaps the activity of type
I 5 alpha reductase is greater than type II activity in one person
but the reverse is true for another. Or one person has more androgen
receptors on the cells in their hair follicles such that small amounts
of androgen hormone has a bigger adverse impact. The extent of hair
loss may be the same in two individuals but the importance of different
androgens and androgen receptors in the development of hair loss
may differ from person to person.
All these subtle differences may mean that a treatment that works
well by acting to block dihydrotestoerone production through 5 alpha
reductase inhibition may work well for one person but will work
less well for another where hair follicles have high numbers of
androgen receptors that can be triggered by comparatively low levels
of dihydrotestosterone.
Why
doesn't propecia always work references
- Lattanand
A, Johnson WC. Male pattern alopecia a histopathologic and histochemical
study. J Cutan Pathol. 1975;2(2):58-70.
- Kligman AM. The comparative histopathology
of male-pattern baldness and senescent baldness. Clin Dermatol.
1988 Oct-Dec;6(4):108-18
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