Description:
Proviron® is Schering’s (now Bayer’s) brand name for the oral androgen mesterolone (1-
methyl dihydrotestosterone). Similar to dihydrotestosterone, mesterolone is a strong
methyl dihydrotestosterone). Similar to dihydrotestosterone, mesterolone is a strong
androgen with only a weak level of anabolic activity. This is due to the fact that like
dihydrotestosterone, mesterolone is rapidly reduced to inactive diol metabolites in muscle
tissue where concentrations of the 3-hydroxysteroid dehydrogenase enzyme are high. The
belief that the weak anabolic nature of this compound indicates a tendency to block the
androgen receptor in muscle tissue, thereby reducing the gains of other more potent musclebuilding
steroids, should likewise not be taken seriously. In fact, due to its extremely high
affinity for plasma binding proteins such as SHBG, mesterolone may actually work to
potentate the activity of other steroids by displacing a higher percentage into a free, unbound
state. Among athletes, mesterolone is primarily used to increase androgen levels when dieting
or preparing for a contest, and as an anti-estrogen due to its intrinsic ability to antagonize the
aromatase enzyme.
History:
According to company literature, Schering developed Proviron® in 1934, making this is an
extremely old medication as far as anabolic/androgenic steroids. Schering also states that it
was the first medication put into clinical practice for the treatment of “hormone-related
diseases and complaints in men. ”Accordingly, mesterolone would have been developed
around the same time as methyltestosterone (1935) and testosterone propionate (1937),
which are both very old agents generally considered obsolete by today’s standards. In spite
of its age, Proviron has a long history of clinical effectiveness and safety, and remains in
widespread clinical use today. It is generally prescribed to males for the treatment of
declining physical and mental capacity caused by age and subnormal androgen levels, low
libido caused by insufficient androgen levels, hypogonadism (in pre- and post-pubescent
males), and infertility (in certain situations mesterolone increases the quality and quantity of
sperm).
The use of mesterolone as a fertility aid is perhaps one of the most controversial indications
for this drug considering that anabolic/androgenic steroids are generally linked to infertility. It
is also a use of mesterolone that is quite often misunderstood by athletes. Mesterolone is
applicable here because it is an effective androgen that offers minimal suppression of
gonadotropins in normal therapeutic doses, not because it increases LH output. Absent
gonadotropin suppression, the drug may supplement androgenicity necessary for sperm
production. It is well understood that androgens have direct stimulatory effects on
spermatogenesis, and also influence the transportation and maturation of sperm via effects on
the epididymis, ductus deferens, and seminal vesicles. So the role of these hormones is not
entirely suppressive. Mesterolone seems to have a unique positive influence on certain cases
of male fertility because its potential stimulatory effects on sperm quantity and quality are not
overridden by the suppression of gonadotropins.
Mesterolone is widely manufactured by Bayer (formerly Schering), which currently sells the
drug in more than thirty countries worldwide. The most common brand name used for its sale
is Proviron, although Schering/Bayer has sold the agent under other names in certain
markets, including Mestoranum and Provironum. Additionally, other manufacturers have sold
mesterolone over the years, appearing under such brand names as Pluriviron (Asche,
Germany), Vistimon (Jenepharm, Germany), and Restore (Brown & Burke, India). In spite
of its long track record of safety and efficacy, mesterolone was never approved for sale in
the United States. It remains available in many Western nations, however. Bayer remains the
major (almost exclusive) global supplier of mesterolone today, although on rare occasion
other brands of the drug can be located.
How Supplied:
Mesterolone is widely available in human drug markets. Composition and dosage may vary
by country and manufacturer; preparations generally contain 25 mg or 50 mg of steroid per
tablet.
Structural Characteristics:
Mesterolone is a modified form of dihydrotestosterone. It differs by the addition of a methyl
group at carbon 1, which helps protect the hormone from hepatic metabolism during oral
administration. The same structural modification is also used with oral Primobolan®
(methenolone) tablets. Alkylation at the one position slows hepatic metabolism of the steroid
during the first pass, although much less profoundly than c-17 alpha alkylation. Mesterolone
during the first pass, although much less profoundly than c-17 alpha alkylation. Mesterolone
is resistant enough to breakdown to allow therapeutically beneficial blood levels to be
achieved, although the overall bioavailability remains much lower than c-17 alpha alkylated
oral steroids. Mesterolone also has a very strong binding affinity for Sex Hormone Binding
Globulin.572 This may act to displace other steroids more weakly bound to SHBG into a free
(active) state.
Side Effects (Estrogenic):
Mesterolone is not aromatized by the body, and is not measurably estrogenic. An antiestrogen
is not necessary when using this steroid, as the drug is unlikely to induce
gynecomastia, water retention, or other estrogen-related side effects.
Mesterolone is actually believed to act as an anti-aromatase in the body, preventing or
slowing the conversion of steroids into estrogen. The result is somewhat comparable to
Arimidex®, although less profound. The anti-estrogenic properties of mesterolone are not
unique, and a number of other steroids have demonstrated similar activity.
Dihydrotestosterone and Masteron (2-methyl-dihydrotestosterone), for example, have been
successfully used as therapies for gynecomastia and breast cancer due to their strong
androgenic and potentially anti-estrogenic effect. It has also been suggested that nandrolone
may even lower aromatase activity in peripheral tissues where it is more resistant to estrogen
conversion (the most active site of nandrolone aromatization seems to be the liver). The antiestrogenic
effect of all of these compounds is presumably caused by their ability to compete
with other substrates for binding to the aromatase enzyme. With the aromatase enzyme
bound to the steroid, yet being unable to alter it, an inhibiting effect is achieved as it is
temporarily blocked from interacting with other hormones.
Side Effects (Androgenic):
Mesterolone is classified as an androgenic steroid. Androgenic side effects are common with
this substance, especially with higher doses. This may include bouts of oily skin, acne, and
body/facial hair growth. Anabolic/androgenic steroids may also aggravate male pattern hair
loss. Women are also warned of the potential virilizing effects of anabolic/androgenic
steroids. These may include a deepening of the voice, menstrual irregularities, changes in skin
texture, facial hair growth, and clitoral enlargement. Additionally, the 5-alpha reductase
enzyme does not metabolize mesterolone, so its relative androgenicity is not affected by
finasteride or dutasteride.
Side Effects (Hepatotoxicity):
Mesterolone is not c17-alpha alkylated, and not known to produce hepatotoxic effects; liver
toxicity is unlikely.
Side Effects (Cardiovascular):
Anabolic/androgenic steroids can have deleterious effects on serum cholesterol. This includes
a tendency to reduce HDL (good) cholesterol values and increase LDL (bad) cholesterol
values, which may shift the HDL to LDL balance in a direction that favors greater risk of
arteriosclerosis. The relative impact of an anabolic/androgenic steroid on serum lipids is
dependant on the dose, route of administration (oral vs. injectable), type of steroid
(aromatizable or non-aromatizable), and level of resistance to hepatic metabolism.
Mesterolone is an oral non-aromatizable androgen, and expected to have a notable negative
effect on lipids. Studies administering 100 mg of mesterolone per day to hypogonadal men
for approximately 6 months demonstrated a significant increase in total cholesterol (18.8%)
and LDL cholesterol (65.2%), accompanied by a significant decrease in HDL cholesterol (-
35.7%).573
Mesterolone should not be used when cardiovascular risk factors preclude the use of other
oral steroids.
To help reduce cardiovascular strain it is advised to maintain an active cardiovascular
exercise program and minimize the intake of saturated fats, cholesterol, and simple
carbohydrates at all times during active AAS administration. Supplementing with fish oils (4
grams per day) and a natural cholesterol/antioxidant formula such as Lipid Stabil or a
product with comparable ingredients is also recommended.