Standard Methyltestosterone (oral)
Chemical Names 7,17-dimethyl-19-norandrost-4-en-3-one-17b-ol, 17beta-Hydroxy-7alpha,17-dimethylestr-4-en-3-one
Estrogenic Activity high
Progestational Activity high
Mibolerone is an oral anabolic steroid, structurally derived from nandrolone. This agent is specifically 7,17-dimethylated nandrolone, significantly more potent as an anabolic and androgenic agent than its non-methylated parent. Over the years, mibolerone has earned a reputation among bodybuilders as being one of the strongest steroids ever made. This is correct in a technical sense, as it is one of only a select few commercial steroid products effective in microgram, not milligram, amounts. During standard animal assays, mibolerone was determined to have 41 times the anabolic activity of methyltestosterone when given orally. In contrast, it had only 18 times the androgenic activity. Although both properties are strongly pronounced with this agent, it retains a primarily anabolic character (in a relative sense). Estrogenic and progestational properties are also very pronounced with this drug, however. Among athletes it is most commonly applied during bulking phases of training, or to stimulate aggression before a workout or competition.
Mibolerone was first described in 1963.430 It was developed into a veterinary medicine during the 1960’s by Upjohn, which sold the drug under the brand name Cheque Drops. The preparation contained 100 mcg/ml of steroid in a 55 mL bottle, for a total steroid content of 5.5 milligrams (illustrating the high relative potency of mibolerone). Pharmacia & Upjohn later also sold a preparation called Cheque Medicated Dog Food, of obvious composition. The drug was administered orally, and had been used to interrupt the estrous cycle of female dogs, preventing them from going into heat. It is approved for use in an animal for no longer than 24 months. Use of the drug is considered carefully by most veterinarians, mainly because longer-term administration can produce side effects such as clitoral enlargement, aggression, urinary difficulties, and liver damage.
Among athletes, mibolerone has always been seen with a high level of mystique, perhaps partly due to its limited availability. Those actually familiar with the Upjohn (then Pharmacia & Upjohn) product were likely disappointed during the early 2000’s, when the Cheque products were officially discontinued by the manufacturer. The company, now Pfizer Animal Health, presently lists no mibolerone-containing products on its inventory, despite retaining the rights to market the drug. Mibolerone is still available in the U.S., but only in generic form from a private compounding pharmacy, obtained under special order by a licensed veterinarian. The removal of the Pharmacia & Upjohn products from the U.S. market marked the commercial end of mibolerone. No prescription preparation, human or veterinary, is currently known to contain mibolerone worldwide.
Mibolerone is no longer available as a prescription drug product. When produced it most commonly came in the form of an oral solution based in propylene glycol, carrying 100mcg of steroid per milliliter in a 55 mL bottle.
Mibolerone is a modified form of nandrolone. It differs by 1) the addition of a methyl group at carbon 17-alpha to protect the hormone during oral administration and 2) the introduction of a methyl group at carbon 7 (alpha), which inhibits 5-alpha reduction and increases relative androgenicity. 7,17-dimethylated steroids also tend to be very resistant to metabolism and serum-binding proteins, greatly enhancing their relative biological activity.
Side Effects (Estrogenic):
Mibolerone is aromatized by the body, and is considered a highly estrogenic steroid due to its conversion to 7,17-dimethylestradiol (an estrogen with high biological activity). Gynecomastia may be a concern during treatment, especially when higher than normal therapeutic doses are used. At the same time water retention can become a problem, causing a notable loss of muscle definition as both subcutaneous water retention and fat levels build. To avoid strong estrogenic side effects, it may be necessary to use an anti-estrogen such as Nolvadex®. One may alternately use an aromatase inhibitor like Arimidex® (anastrozole), which is a more effective remedy for estrogen control. Aromatase inhibitors, however, can be quite expensive in comparison to standard estrogen maintenance therapies, and may also have negative effects on blood lipids.
It is of note that mibolerone also displays strong activity as a progestin in the body. The side effects associated with progesterone are similar to those of estrogen, including negative feedback inhibition of testosterone production and enhanced rate of fat storage. Progestins also augment the stimulatory effect of estrogens on mammary tissue growth. There appears to be a strong synergy between these two hormones here, such that gynecomastia might even occur with the help of progestins without excessive estrogen levels being present. The use of an anti-estrogen, which inhibits the estrogenic component of this disorder, is often sufficient to mitigate gynecomastia caused by mibolerone.
Side Effects (Androgenic):
Although classified as an anabolic steroid, androgenic side effects are still common with this substance. This may include bouts of oily skin, acne, and body/facial hair growth. Anabolic/androgenic steroids may also aggravate male pattern hair loss. Individuals sensitive to the androgenic effects of this steroid may find a milder anabolic such as Deca-Durabolin® to be more comfortable. Women are additionally 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. Note that 7-methylation inhibits steroid 5-alpha reduction.431 The relative androgenicity of mibolerone is not affected by the concurrent use of finasteride or dutasteride.
Side Effects (Hepatotoxicity):
Mibolerone is a c17-alpha alkylated compound. This alteration protects the drug from deactivation by the liver, allowing a very high percentage of the drug entry into the bloodstream following oral administration. C17-alpha alkylated anabolic/androgenic steroids can be hepatotoxic. Prolonged or high exposure may result in liver damage. In rare instances life-threatening dysfunction may develop. It is advisable to visit a physician periodically during each cycle to monitor liver function and overall health. Intake of c17-alpha alkylated steroids is commonly limited to 6-8 weeks, in an effort to avoid escalating liver strain. Severe liver complications are rare given the periodic nature in which most people use oral anabolic/androgenic steroids, although cannot be excluded with this steroid, especially with high doses and/or prolonged administration periods. Note that U.S. prescribing information for Cheque Drops mentions only one human study being conducted on mibolerone, and that the study was terminated early due to high hepatotoxicity.
The use of a liver detoxification supplement such as Liver Stabil, Liv-52, or Essentiale Forte is advised while taking any hepatotoxic anabolic/androgenic steroids.
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. Mibolerone has a strong effect on the hepatic management of cholesterol due to its structural resistance to liver breakdown and route of administration. Anabolic/androgenic steroids may also adversely affect blood pressure and triglycerides, reduce endothelial relaxation, and support left ventricular hypertrophy, all potentially increasing the risk of cardiovascular disease and myocardial infarction.
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):
All anabolic/androgenic steroids when taken in doses sufficient to promote muscle gain are expected to suppress endogenous testosterone production. Without the intervention of testosterone-stimulating substances, testosterone levels should return to normal within 1-4 months of drug secession. Note that prolonged hypogonadotrophic hypogonadism can develop secondary to steroid abuse, necessitating medical intervention.
The above side effects are not inclusive. For more detailed discussion of potential side effects, see the Steroid Side Effects section of this book.
Studies have shown that taking an oral anabolic steroid with food may decrease its bioavailability.432 This is caused by the fat-soluble nature of steroid hormones, which can allow some of the drug to dissolve with undigested dietary fat, reducing its absorption from the gastrointestinal tract. For maximum utilization, this steroid should be taken on an empty stomach.
Mibolerone was never approved for use in humans. Prescribing guidelines are unavailable. In the athletic arena, the drug is used intermittently due to its high level of hepatotoxicity, with cycles usually lasting no more than 6 weeks followed by 6-8 weeks off. A daily dosage of 200 to 500mcg is most common for bodybuilding purposes. This level is typically sufficient for gains in strength and muscle mass (bulk). The high progestational and estrogenic activity of mibolerone makes it of little value in speed and endurance sports, causing an unwanted retention of water weight.
Mibolerone was never approved for use in humans. Prescribing guidelines are unavailable. Mibolerone is generally not recommended for women for physique- or performance-enhancing purposes due to its very strong nature and tendency to produce virilizing side effects.
Mibolerone is sold in the U.S. as a compounded veterinary medicine only. No commercial preparations containing this drug are known to exist worldwide. Mibolerone remains available on the black market in underground preparations only.
430. Lyster SC, et al. Acta Endocrin (Kbh) 43 (1963):399.
431. The biological activity of 7 alpha-methyl-19-nortestosterone is not amplified in male reproductive tract as is that of testosterone. Endocrinology.
1992 Jun; 130(6):3677-83.
432. Anabolic Steroids and Sports Volume II. James E. Wright. Sports Science Consultants, Natick, MA 1982.