Mesterolone is an androgen receptor agonist which was developed for hormone replacement therapy in males suffering from androgen deficiency and related disorders. Mesterolone is known under the name Proviron. The drug is also used by bodybuilders and athletes.

Mesterolone:
https://drugs.ncats.io/drug/0SRQ75X9I9

Mesterolone is used to treat androgen deficiency in male hypogonadism and to help support male fertility. It is also used to treat delayed puberty in boys. In these disorders, the body doesn't produce enough male hormones naturally. This drug helps to address that and treat it.

It is also used as an estrogen inhibitor. A very common side effect of steroids is that the way they are metabolized if they are taken in excess - which is usually the case, they create estrogen as a by-product. This leads to two of the most well-known side effects of taking steroids, steroid gut and enlargement of breast tissue. Using Mesterolone helps inhibit and in some cases block estrogen production which makes it ideal for stacking with other steroids. It is also used by bodybuilders to increase muscle hardness, libido, improve sexual health and provide an overall sense of well-being.

Ultimately, it's not exactly a natural product which means it comes with a lot of cautionary points that need to be taken into consideration if you are at all giving Mesterolone a thought. The very first thing to keep in mind is that there are several factors that affect the effectiveness of Mesterolone. Age and weight are the most obvious ones, but one of the most important factors to keep in mind is the way it might interact with other steroids or even medication that might be prescribed. Since it is a chemical, there are chances that it might react both positively and negatively with other medication, steroids, and supplements that one might be taking.

Mesterolone (Proviron) Review - Pro's & Con's (Updated July 2019):
https://www.swolhq.com/mesterolone/

Weak Anabolic Activity:
Proviron is the trade / brand name for the androgen known as Mesterolone. It is an oral product, and is not considered an anabolic steroid. This is because its anabolic activity is known for being extremely weak - so weak, in fact, that it can be practically considered nonexistent. Although Proviron is considered a very old medication, it still stands the test of time as being known as a compound that has impressive effectiveness as a medicine alongside an impressive history of safety and tolerance among patients. Within the medical establishment, Proviron has been utilized as a medication for the treatment of declining well-being in older males due to declining androgen levels, libido dysfunction in males, and infertility. Its use as a fertility aid is where Proviron was really emphasized in medical literature. This is because while almost all anabolic/androgenic steroids are known to cause temporary infertility, Proviron in normal therapeutic dosages actually barely suppresses endogenous gonadotropins (LH and FSH) when utilized. However, Proviron is poorly misunderstood as a compound that increases LH, which it does not do. Instead, research has demonstrated that Proviron provides the androgenic effects necessary for spermatogenesis in specific areas in the testes. Schering still manufactures Mesterolone under the name of Proviron across the world today. It has been sold under different brand names as well, including Pluriviron (in Germany by Asche), Vistimon (in Germany by Jenepharm), and Restore (in India, by Brown and Burke).

What is interesting, however, is that Proviron was never approved for use on the prescription market in the United States.

Proviron History and Overview:
https://www.steroidal.com/steroid-profiles/proviron-mesterolone/

Proviron has four distinct uses in the world of bodybuilding:

1. The first being the result of its structure. It is 5-alpha reduced and not capable of forming estrogen, yet it nonetheless has a much higher affinity for the aromatase enzyme (which converts testosterone to estrogen) than testosterone does. That means in administering it with testosterone or another aromatizable compound, it prevents estrogen build-up because it binds to the aromatase enzyme very strongly, thereby preventing these steroids from interacting with it and forming estrogen.
2. The second use is in enhancing the potency of testosterone. Testosterone in the body at normal physiological levels is mostly inactive. As much as 97 or 98 percent of testosterone in that amount is bound to sex hormone binding globulin (SHBG) and albumin, two proteins. In such a form testosterone is mostly inactive. But as with the aromatase enzyme, DHT has a higher affinity for these proteins than testosterone does, so when administered simultaneously the mesterolone will attach to the SHBG and albumin, leaving larger amounts of free testosterone to mediate anabolic activities such as protein synthesis.
3. Thirdly, mesterolone is added in pre-contest phases to increase a distinct hardness and muscle density. Probably due to its reduction in circulating estrogen, perhaps due to the downregulating of the estrogen receptor in muscle tissue, it decreases the total water build-up of the body giving its user a much leaner look, and a visual effect of possessing "harder" muscles with more cuts and striations. Proviron is often used as a last-minute secret by a lot of bodybuilders and both actors and models have used it time and again to deliver top shape day in day out, when needed.
4. Lastly Proviron is used during a cycle of certain hormones such as nandrolone, with a distinct lack of androgenic nature, or perhaps 5-alpha reduced hormones that don't have the same affinities as DHT does. Such compounds, thinking of trenbolone, nandrolone and such in particular, have been known to decrease libido. Limiting the athlete to perform sexually being the logical result.

Who has run proviron? Questions...
https://www.bluelight.org/xf/threads/who-has-run-proviron-questions.712030/

Testosterone Enhancer:
Proviron on its own is considered to be a weak steroid according to a study by A.T. Kicman published in the British Journal of Pharmacology. However, it has unique properties that make it a useful and effective enhancer, especially of testosterone. In normal levels in the body, testosterone is mostly inactive because most of it is bound by sex hormone binding globulin (SHBG) and albumin. Proviron also has a great affinity for SHBG, so when administered, it will bind to the SHBG, leaving more testosterone free. The increase in free testosterone can then mediate anabolic activities, including protein synthesis, which in turn increases muscle gain. Estrogen is only active and effective when bound to estrogen receptors. Proviron decreases the ability of these estrogen receptors, found in the muscles, to bind to estrogen, therefore decreasing the amount of active estrogen.

Positive Effects of Proviron:
https://www.livestrong.com/article/67681-positive-effects-proviron/

Anti-Estrogenic Activity:
Proviron (mesterolone) is an interesting anabolic steroid, though it is not of much value to bodybuilding. It seems that the most common reason for many to consider including it in a steroid stack is for anti-estrogenic activity. In the days before anti-aromatases and the use of SERMs (selective estrogen receptor modulators) such as Clomid and Nolvadex, there was some merit to this. An amount of aromatizing steroid marginally over the amount that would be tolerable without Proviron became tolerable with the inclusion of it. However, the effect is indeed only marginal, and much better anti-estrogenic agents now exist. When these are used, there is no need for Proviron as an anti-estrogen.

Proviron has an androgenic effect that in many cases improves libido. However, most anabolic steroids also have this same property. In a steroid cycle, adding Proviron accomplishes nothing further. Or in the case of anabolic steroids such as nandrolone (Deca) which for other reasons may adversely affect libido, Proviron provides no greater help against that than do various other anabolic steroids.

Another interesting thing is that it enjoys some practical use as a pro-sexual agent inbetween cycles. Typically 50 mg is taken shortly before improved performance is expected to be useful. Contrary to common belief, Proviron is somewhat inhibitory of the HPTA. Using it during the recovery phase as part of post-cycle therapy is counterproductive. It is also inadvisable for this reason to use it continuously while intending to be off-cycle, but occasional recreational use presents no problem. Unlike almost all other orals, Proviron is not hepatotoxic, as it is not 17-alkylated.

Proviron - Mesterolone - Anabolic steroids:
https://thinksteroids.com/steroid-profiles/proviron/

Proviron has no effect on the body's own testosterone production:
Proviron is a synthetic, orally effective androgen which does not have any anabolic characteristics. Proviron is used in school medicine to ease or cure disturbances caused by a deficiency of male sex hormones. Many athletes, for this reason, often use Proviron at the end of a steroid treatment in order to increase the reduced testosterone production. This, however is not a good idea since Proviron has no effect on the body's own testosterone production but-as mentioned in the beginning-only reduces or completely eliminates the dysfunctions caused by the testosterone deficiency. These are in particular impotence which is mostly caused by an androgen deficiency that can occur after the discontinuance of steroids, and infertility which manifests itself in a reduced sperm count and a reduced sperm quality. Proviron is therefore taken during a steroid administration or after discontinuing the use of the steroids, to eliminate a possible impotency or a reduced sexual interest. This, however does not contribute to the maintenance of strength and muscle mass after the treatment. There are other better suited compounds for this. For this reason Proviron is unfortunately considered by many to be a useless and unnecessary compound. You should be aware that Proviron is also an estrogen antagonist which prevents the aromatization of steroids.

Mesterolone Specifications:
http://www.bionutritionpharma.com/anti-estrogen/mesterolone.html

Does not Aromatize into Estrogen:
Just as with DHT, the activity of this steroid is that of a strong androgen which does not aromatize into estrogen. In clinical situations Proviron is generally used to treat various types of sexual dysfunction, which often result from a low endogenous testosterone level. It can usually reverse problems of sexual disinterest and impotency, and is sometimes used to increase the sperm count. The drug does not stimulate the body to produce testosterone, but is simply an oral androgen substitute that is used to compensate for a lack of the natural male androgen. Although this steroid is strongly androgenic, the anabolic effect of it is considered too weak for muscle building purposes. This is due to the fact that Proviron is rapidly reduced to inactive metabolites in muscle tissue, a trait also characteristic of dihydrotestosterone. If money and availability does not prevent it, Arimidex is actually a much better choice than Proviron though. This drug was designed specifically as an antiaromatase..

Proviron:
https://medium.com/@cemkara_22584/proviron-is-the-schering-brand-name-for-the-oral-androgen-mesterolone-1-methyl-8344ba74e74e

Side Effects:
Mesterolone can be fatal if you are pregnant or planning on becoming pregnant, or breastfeeding and hence, you should not take it under such conditions. It should also be avoided if you have a condition or have a history of very high calcium levels, high blood pressure, diabetes, migraine, heart or kidney problems, or if you are allergic to it or any of its components. If you are a patient of prostate cancer, breast cancer and tumor in liver then you are advised against using it. The common side effects of Mesterolone are oily skin, male pattern baldness, acne, facial hair growth or body hair growth, persistent or frequent erection of penis, fluid retention, breast enlargement, depression or aggression. It is advised to stop intake of Mesterolone and see a doctor immediately if you encounter any of these conditions. Females are advised against taking this male hormone.

Mesterolone Overview:
https://www.lybrate.com/medicine/mesterolone

Major & minor side effects for Mesterolone:

• Itching
• Fever
• Rash
• Hives
• Abdominal pain
• Indigestion
• Nausea
• Vomiting

Medicine Info > Mesterolone:
https://www.practo.com/medicine-info/mesterolone-1420-api

What are the Drug Interactions of Mesterolone?
Mesterolone should be avoided with:
Immunosuppressant drug like cyclosporin which decreases immunity. Drugs used in the treatment of diabetes. Thyroxine which is used to replace low thyroid levels. Anticoagulants like warfarin which is used to treat blood clots. Drugs like phenytoin or phenobarbital used to treat seizures since they reduce the levels of mesterolone. Neuromuscular blockers which are used for temporary paralysis of skeletal muscles as they might cause resistance to treatment.

Mesterolone Drug Information:
https://www.medindia.net/doctors/drug_information/mesterolone.htm

Sperm Count:
Question: What is the role of mesterolone in increasing the sperm count and motility and what is the mechanism by which it increases?

Answer: Gonadotrophin releasing hormone is the hormone that controls reproductive function. It is produced and released by a part of the brain called the hypothalamus and in turn controls the production and release of luteinising hormone and follicle stimulating hormone (called gonadotrophins) from the adjacent pituitary gland. Luteinising hormone acts with follicle stimulating hormone to stimulate testosterone production, secreted by the interstitial cells of the testis and responsible for triggering the development of sperm and of many sexual characteristics such as the changes that occur during puberty in the penis and testicles. Mesterolone is indicated in the treatment of testosterone deficiency or male infertility associated with malfunction of the hypothalamus, pituitary or testicles. Mesterolone's molecular structure gives it special properties that set it apart from testosterone and all the drugs derived from testosterone that are used for this type of therapy, in that it is not broken down by the body (metabolised) to oestrogen. This difference almost certainly accounts for the findings that, in its usual therapeutic dosage in normal men, mesterolone does not significantly depress the release of gonadotrophins from the pituitary. Therefore sperm production (spermatogenesis) is unimpaired by mesterolone when compared with other drugs used in this area, which suppress and therefore replace the body's natural (endogenous) testosterone.

In other words, Mesterolone supplements ones natural testosterone.

Mesterolone Q and A:
https://www.netdoctor.co.uk/ask-the-expert/babies-children/a11969/mesterolone/

A synthetic anabolic androgenic steroid with reported abuses in human sports.

• Also a potential doping agent in equine sports.
• Mesterolone has been used in the treatment of primary nocturnal enuresis in boys six to ten years of age.
• Mesterolone has been utilized in hypogonadism patients to increase total ejaculation volume and the concentration of fructose in the spermatic plasma to normal levels.
• Mesterolone treatment decreases cholesterol, beta-lipoproteins, fatty acid esters, free fatty acids, triglycerides and glycerol in human serum.
• Belongs to the class of organic compounds known as androgens and derivatives.
  • They are known to favor the development of masculine characteristics.
  • They also show profound effects on scalp and body hair in humans.

Metabocard for Mesterolone:
http://www.hmdb.ca/metabolites/HMDB0006036

Proviron Package Insert (PDF 3 pages):
https://www.bayer.co.za/static/documents/MSDS/PIs/PROVIRON_EN_PI.pdf

Proviron Tablets Package Leaflet:
https://www.nps.org.au/medicine-finder/proviron-tablets

Proviron Information:
https://www.healthdirect.gov.au/medicines/brand/amt,35984011000036102/proviron

Proviron Tablets Leaflet:
https://mydr.com.au/medicines/proviron-tablets

Mesterolone Monograph:
http://www.inchem.org/documents/pims/pharm/pim904.htm

Mesterolone Safety Data Sheet (PDF 6 pages):
https://www.caymanchem.com/msdss/21171m.pdf