Mibolerone is a synthetic oral anabolic-androgenic steroid, chemically 7α,17α-dimethyl-19-nortestosterone. It was marketed by Upjohn as a veterinary drug, Cheque Drops, an oral liquid used to prevent heat (estrus) in adult female dogs. It has never been approved for use in people.
That is the most important fact about it: every efficacy and safety study of mibolerone was done in dogs, cats, rats or cell culture. No controlled human trial exists, and we found no published human pharmacokinetic data. In the laboratory, mibolerone is best known as a high-affinity research ligand for measuring androgen receptors.
This page summarizes what the US animal-drug regulations, veterinary studies and laboratory research report. It is for education only and is not medical advice.
| Property | Detail |
|---|---|
| Drug class | 17α-alkylated anabolic-androgenic steroid (19-nortestosterone derivative) |
| Product | Cheque Drops (NADA 102-709); also a mibolerone-medicated dog food (NADA 107-347); sponsor now Zoetis |
| Approved species and use | Adult female dogs only, to prevent estrus; prescription (veterinarian) only |
| Route and strength | Oral liquid, 100 µg/mL |
| Labeled dog dose | 30–180 µg once daily, by body weight |
| Human approval | None; no controlled human trials |
| Half-life | Not established in humans; no published value found |
| Receptor binding | Androgen and progesterone receptors; no appreciable binding to SHBG |
| US status | Schedule III controlled substance |
| WADA status | Prohibited at all times (S1.1, named) |
What it is
Mibolerone’s formula is C₂₀H₃₀O₂, molecular weight 302.5 g/mol (PubChem). The DEA lists it by its chemical name, 7α,17α-dimethyl-17β-hydroxyestr-4-en-3-one (21 CFR 1308.13). It builds on nandrolone (19-nortestosterone, the parent of Deca-Durabolin) with two added methyl groups:
| Change from nandrolone | What it means |
|---|---|
| 17α-methyl group | The same change used in methyltestosterone and other oral steroids. It slows breakdown in the liver so the drug works by mouth, and the 17α-alkylated class is the one most linked to liver toxicity. |
| 7α-methyl group | 7α-methyl-19-nortestosterone (MENT), which shares this group, is a high-potency androgen whose potency was tied mainly to its high androgen receptor affinity (Kumar et al., J Steroid Biochem Mol Biol 1999). |
Because it binds the androgen receptor tightly and resists metabolism, tritium-labeled mibolerone became a standard tool for counting androgen receptors in prostate and other tissues (Schilling and Liao, Prostate 1984). In that work it was more selective for the androgen receptor than methyltrienolone (R1881), the other common research ligand.
Androgen and progestin activity
Laboratory studies show that mibolerone is not a pure androgen:
- Androgen receptor. In rat prostate and uterus it bound the androgen receptor specifically and with high affinity (Traish et al., Endocrinology 1986).
- Progesterone receptor. In calf uterus and human breast tumor tissue it also bound the progesterone receptor. It did not bind the glucocorticoid receptor.
- SHBG. Unlike DHT, it showed no appreciable binding to human sex hormone-binding globulin (SHBG), the blood protein that carries testosterone.
- Progestin-like effects in cells. In human breast cancer cells, mibolerone produced progesterone-receptor-mediated effects at nanomolar to picomolar concentrations (Markiewicz and Gurpide, 1997). Another cell study concluded it has “both androgenic and progestagenic actions” (Cops et al., J Steroid Biochem Mol Biol 2008).
About potency claims. Online sources often describe mibolerone with very large anabolic and androgenic ratings relative to methyltestosterone. We found no primary publication behind these numbers, so we do not repeat them. What the record does show is that the approved dog doses are measured in micrograms, not milligrams.
We also found no primary study that measured whether mibolerone is converted to an estrogen in the body, so this page makes no claim either way.
How it works in the body
There are no human pharmacokinetic studies. The available data come from animals and liver preparations:
| Finding | Species / system | Source |
|---|---|---|
| Serum levels depended on the formulation, which also changed time to peak; levels differed in the same dogs at two locations | Beagle dogs | Krzeminski et al., Am J Vet Res 1978 |
| Main metabolites were monohydroxylated and oxidized mibolerone | Beagle liver microsomes | Williams et al., J Vet Pharmacol Ther 2000 |
| After 1 mg/kg by mouth, urinary metabolites were mainly glucuronide conjugates; sulfate conjugation was minor | Greyhound dogs | Williams et al., J Vet Pharmacol Ther 2000 |
| Stable to metabolism in the prostate | Rat | Schilling and Liao 1984 |
| Prostate uptake 0.56% of injected dose per gram at 1 hour; prostate-to-blood ratio above 10 at 2–4 hours | Castrated rats | Carlson and Katzenellenbogen, J Steroid Biochem 1990 |
In cats, the study authors concluded that mibolerone prevents estrus by suppressing pituitary release of luteinizing hormone (LH), the signal that drives the ovaries (Burke et al., Am J Vet Res 1977).
Approved veterinary use
US animal-drug regulations list two mibolerone products, both now sponsored by Zoetis. Ownership moved from Pharmacia & Upjohn (part of Pfizer) to Zoetis in 2014 (79 FR 28813; 79 FR 13542).
| Product | Form | Maximum duration | Regulation |
|---|---|---|---|
| Cheque Drops | Oral liquid, 100 µg/mL, given by mouth or in a little food | 24 months | 21 CFR 520.1430 |
| Cheque medicated dog food | 6.5 oz can with 30 or 60 µg | 12 months | 21 CFR 558.348 |
The only labeled indication is preventing estrus in adult female dogs not intended primarily for breeding. For Cheque Drops, dosing starts at least 30 days before the expected heat and is given daily (the medicated-food dosing is similar):
| Dog body weight | Daily dose |
|---|---|
| 1–25 lb | 30 µg |
| 26–50 lb | 60 µg |
| 51–100 lb | 120 µg |
| Over 100 lb, or German Shepherds and German Shepherd mixes | 180 µg |
The medicated-food regulation adds limits: no use before a dog’s first heat, no use in purebred Bedlington terriers, and oral use in adult female dogs only. Both products are restricted to use by or on the order of a licensed veterinarian.
What the research shows
All of the efficacy data below come from animals. None of it measures muscle, strength or performance in people.
Estrus prevention in dogs
An early study screened several steroidal and nonsteroidal compounds for preventing heat in dogs. Mibolerone was effective and appeared safe, while the others lacked efficacy, had extensive side effects, or both (Sokolowski and Zimbelman, Am J Vet Res 1976). A longer Beagle study then tested it for up to 730 days (Sokolowski and Geng, Am J Vet Res 1977):
| Daily dose | Result |
|---|---|
| 20 µg | Prevented estrus in 70% of dogs |
| 60 µg (immature dogs) | Inhibited estrus |
| 200 µg (mature dogs) | Inhibited estrus |
Other findings in that study:
- vaginal discharge;
- a dose-related increase in clitoral size;
- a lower conception rate after treatment, seen only in dogs given 20 µg daily for 730 days;
- grossly normal pups born to dogs that conceived after treatment.
In a separate study lasting about 16 months, exposure to adult male dogs did not break through the estrus suppression (Sokolowski, JAVMA 1978).
False pregnancy in dogs
A blinded, placebo-controlled field trial treated 63 dogs with false pregnancy (pseudopregnancy) for 5 days at 0.008, 0.016 or 0.025 mg/kg/day, with 17 dogs on placebo (Brown, JAVMA 1984). Improvement in behavioral and physical signs differed significantly by dose, and 0.016 mg/kg/day was estimated as the best dose. This is not a labeled US indication.
Cats
In a 280-day study in domestic cats, 50 µg daily for 180 days prevented estrus (Burke et al., Am J Vet Res 1977). Lower or less frequent doses did not:
| Regimen | Prevented estrus? |
|---|---|
| 20 µg daily | No |
| 50 µg once weekly | No |
| 50 µg daily | Yes |
Cats are not a labeled species in the US regulations.
Side effects and risks
Mibolerone has no human safety data. What is known comes from animal studies and from what is established for its chemical class.
Masculinization
Mibolerone is a potent androgen, and the animal studies consistently found masculinizing effects:
- Dogs: a dose-related increase in clitoral size (Sokolowski and Geng 1977).
- Cats: clitoral enlargement and thickening of the cervical dermis after 3 months at 20 or 50 µg daily (Burke et al. 1977).
- Exposure in pregnancy: when pregnant Beagles were given 20 or 60 µg daily until weaning, their female pups were masculinized; male pups showed no gross effects (Sokolowski and Kasson, Am J Vet Res 1978).
Long-term findings in animals
- Ovarian tumors in dogs. A dog study ended after 9.6 years. Benign ovarian fibromas were found in 12 of 92 dogs given about the effective dose, compared with none of 60 control dogs and none of 55 dogs on exaggerated doses. The tumors showed no invasion or spread (Seaman, Toxicol Pathol 1985).
- Thyroid changes in cats. Treated cats had dose- and time-related changes in serum cholesterol, thyroid weight and thyroid tissue, without clinical signs of thyroid disease over 6 months (Burke et al. 1977).
Liver risk of the 17α-alkylated class
No human liver data exist for mibolerone itself. It does, however, carry the 17α-alkyl group that makes oral steroids harder for the liver to clear. Reviews describe this class as causing raised liver enzymes, cholestasis (blocked bile flow), peliosis (blood-filled cysts in the liver), adenomas and carcinomas (Niedfeldt, Curr Sports Med Rep 2018; Nieschlag and Vorona, Rev Endocr Metab Disord 2015). The same reviews describe broader anabolic steroid risks, including unfavorable lipid changes, raised hematocrit and clotting, heart problems and psychiatric effects.
Hormonal suppression
The only direct evidence on hormone suppression is the cat study’s conclusion that mibolerone works by suppressing LH release. Its effect on LH, natural testosterone production or sperm output has never been measured in humans.
Legal status and use outside medicine
- US controlled substance. Mibolerone is named in Schedule III (21 CFR 1308.13).
- Sport. It is listed by name under S1.1 anabolic androgenic steroids, prohibited at all times in and out of competition (WADA 2026 Prohibited List).
- Animal racing. Researchers characterized its urinary metabolites in greyhounds because androgens used to prevent estrus in racing dogs can also be misused for performance, and testing laboratories need markers to detect them (Williams et al. 2000).
Any mibolerone taken by people comes from outside approved human medicine. There is no human dose, label or safety monitoring standard to refer to.
Key takeaways
- A veterinary drug, never a human one. Mibolerone was approved only to prevent heat in adult female dogs, as Cheque Drops and a medicated dog food.
- No human trials. All efficacy and safety data come from dogs, cats, rats and cell studies, and no human half-life has been published.
- Extremely potent at tiny doses. Labeled dog doses are 30–180 µg per day, and it binds both androgen and progesterone receptors.
- Clear masculinizing effects in animals. Clitoral enlargement in dogs and cats, and masculinized female offspring after exposure in pregnancy.
- A 17α-alkylated steroid. It belongs to the oral steroid class most associated with liver injury, though no mibolerone-specific human liver data exist.
- Controlled and banned in sport. Schedule III in the US and named on the WADA prohibited list.
Sources
- National Center for Biotechnology Information. PubChem Compound Summary for CID 251636, Mibolerone. PubChem.
- Drug Enforcement Administration. Schedules of controlled substances: Schedule III. 21 CFR 1308.13. eCFR.
- Food and Drug Administration. Oral dosage form new animal drugs: Mibolerone. 21 CFR 520.1430. eCFR.
- Food and Drug Administration. New animal drugs for use in animal feeds: Mibolerone. 21 CFR 558.348. eCFR.
- Food and Drug Administration. Oral dosage form new animal drugs; change of sponsor. Federal Register. May 20, 2014;79:28813 (FR Doc 2014-10415). Federal Register.
- Food and Drug Administration. New animal drugs; change of sponsor. Federal Register. March 11, 2014;79:13542 (FR Doc 2014-04937). Federal Register.
- World Anti-Doping Agency. The 2026 Prohibited List: International Standard. WADA 2026 Prohibited List.
- Schilling K, Liao S. The use of radioactive 7 alpha, 17 alpha-dimethyl-19-nortestosterone (mibolerone) in the assay of androgen receptors. Prostate. 1984;5(6):581–588. PubMed.
- Traish AM, Müller RE, Wotiz HH. Binding of 7 alpha, 17 alpha-dimethyl-19-nortestosterone (mibolerone) to androgen and progesterone receptors in human and animal tissues. Endocrinology. 1986;118(4):1327–1333. PubMed.
- Markiewicz L, Gurpide E. Estrogenic and progestagenic activities of physiologic and synthetic androgens, as measured by in vitro bioassays. Methods Find Exp Clin Pharmacol. 1997;19(4):215–222. PubMed.
- Cops EJ, Bianco-Miotto T, Moore NL, et al. Antiproliferative actions of the synthetic androgen, mibolerone, in breast cancer cells are mediated by both androgen and progesterone receptors. J Steroid Biochem Mol Biol. 2008;110(3-5):236–243. PubMed.
- Kumar N, Crozat A, Li F, et al. 7alpha-methyl-19-nortestosterone, a synthetic androgen with high potency: structure-activity comparisons with other androgens. J Steroid Biochem Mol Biol. 1999;71(5-6):213–222. PubMed.
- Carlson KE, Katzenellenbogen JA. A comparative study of the selectivity and efficiency of target tissue uptake of five tritium-labeled androgens in the rat. J Steroid Biochem. 1990;36(6):549–561. PubMed.
- Krzeminski LF, Sokolowski JH, Dunn GH, et al. Serum concentrations of mibolerone in Beagle bitches as influenced by time, dosage form, and geographic location. Am J Vet Res. 1978;39(4):567–572. PubMed.
- Williams TM, Kind AJ, Hill DW. Drug metabolism: in vitro biotransformation of anabolic steroids in canines. J Vet Pharmacol Ther. 2000;23(2):57–66. PubMed.
- Williams TM, Kind AJ, Hyde WG, et al. Characterization of urinary metabolites of testosterone, methyltestosterone, mibolerone and boldebone in greyhound dogs. J Vet Pharmacol Ther. 2000;23(3):121–129. PubMed.
- Sokolowski JH, Zimbelman RG. Evaluation of selected compounds for estrus control in the bitch. Am J Vet Res. 1976;37(8):939–941. PubMed.
- Sokolowski JH, Geng S. Biological evaluation of mibolerone in the female Beagle. Am J Vet Res. 1977;38(9):1371–1376. PubMed.
- Sokolowski JH. Evaluation of estrous activity in bitches treated with mibolerone and exposed to adult male dogs. J Am Vet Med Assoc. 1978;173(8):983–984. PubMed.
- Sokolowski JH, Kasson CW. Effects of mibolerone on conception, pregnancy, parturition, and offspring in the Beagle. Am J Vet Res. 1978;39(5):837–839. PubMed.
- Brown JM. Efficacy and dosage titration study of mibolerone for treatment of pseudopregnancy in the bitch. J Am Vet Med Assoc. 1984;184(12):1467–1468. PubMed.
- Burke TJ, Reynolds HA, Sokolowski JH. A 280-day tolerance-efficacy study with mibolerone for suppression of estrus in the cat. Am J Vet Res. 1977;38(4):469–477. PubMed.
- Seaman WJ. Canine ovarian fibroma associated with prolonged exposure to mibolerone. Toxicol Pathol. 1985;13(3):177–180. PubMed.
- Niedfeldt MW. Anabolic steroid effect on the liver. Curr Sports Med Rep. 2018;17(3):97–102. PubMed.
- Nieschlag E, Vorona E. Doping with anabolic androgenic steroids (AAS): adverse effects on non-reproductive organs and functions. Rev Endocr Metab Disord. 2015;16(3):199–211. PubMed.