Proviron is Schering’s (now Bayer’s) brand name for the oral androgen mesterolone (1-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 muscle-building 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.
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.
Proviron 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.
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 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 anti-estrogen 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 anti-estrogenic 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.
Side Effects (Testosterone Suppression):
Mesterolone has a very weak suppressive effect on gonadotropins and serum testosterone. Studies show that when given in moderate doses (150 mg per day or less), significant suppression of testosterone levels does not occur.574 In studies with higher doses (300 mg per day and above), the agent strongly suppressed serum testosterone.575
The above side effects are not inclusive. For more detailed discussion of potential side effects, see the Steroid Side Effects section of this book.
To treat androgen insufficiency, Proviron is usually given in a dose of 1 tablet (25 mg) three times per day at the initiation of therapy. The drug is later continued at a lower maintenance dose, which usually consists of taking 1 tablet (25 mg) one to two times per day. Similar doses are used to support male fertility, usually in conjunction with other fertility drugs like injectable FSH. The usual dosage among male athletes is between 50 mg and 150 mg of mesterolone per day, or two to six 25 mg tablets. The drug is typically taken in cycles of 6-12 weeks in length, which is usually a sufficient period of time to notice the benefits of drug therapy.
Many bodybuilders favor the use of mesterolone during dieting phases or contest preparation, when low estrogen and high androgen levels are particularly desirable. This is especially beneficial when anabolics like Winstrol®, Anavar, or Primobolan® are being used alone, as the androgenic content of these drugs is relatively low. Mesterolone can be effectively used here to adjust the androgen to estrogen ratio upwards, bringing about an increase in the hardness and density of the muscles, supporting libido and general sense of well being, and increasing the tendency to burn body fat. It is also commonly used (at a similar dosage) to prevent gynecomastia when other aromatizable steroids are being administered, often in conjunction with 10-20 mg per day of Nolvadex.
Proviron is not approved for use in women. This agent is not recommended for women for physique- or performance-enhancing purposes due to its strong androgenic nature and tendency to produce virilizing side effects. Some women do favor the drug, however, and find a single 25 mg tablet enough to efficiently shift the hormone balance in the body, greatly impacting the look of definition to the physique. Intake is usually limited to no longer than four or five weeks in such situations to minimize the chance of developing lasting virilizing effects. One tablet used in conjunction with 10 or 20 mg of Nolvadex® can be even more efficient for muscle hardening, creating an environment here the body is much more inclined to burn off extra body fat, especially in female trouble areas like the hips and thighs. Extreme caution should be taken with such use, however.
Mesterolone remains widely available, the vast majority of products made by or under license from Bayer; most commonly under the Proviron trade name.