Methyltestosterone
17beta-Hydroxy-17alpha-methylandrost-4-ene-3-one
Also known as: Android · Methitest · Testred · Virilon · Orandrone · NSC-9701 · 17-alpha-methyltestosterone
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Alopecia X (when melatonin fails) | 1 mg/kg to a maximum dose of 30 mg (total dose) | PO | once daily | Stop after maximal hair re-growth is noted | 🌎 NA |
| Testosterone-responsive dermatosis | 1 mg/kg to a maximum dose of 30 mg | PO | every other day | Once dog responds, then every 4-7 days | 🌎 NA |
| Suppress estrus in Greyhounds | 5 mg (total dose) | PO | once weekly or divided, two times a week | — | 🌎 NA |
| Estrus suppression | 25-50 mg (total dose) | PO | twice weekly | — | 🌎 NA |
| Anti-estrogenic activity, anabolic effects, negative feedback on gonadotropin release | 0.5 mg/kg | PO | once daily | — | 🌎 NA |
- Alopecia X (when melatonin fails): Get baseline liver profile and then again one and two months after starting treatment. Can cause hepatotoxicity, aggressive behavior and/or seborrhea.
- Anti-estrogenic activity, anabolic effects, negative feedback on gonadotropin release: Dose may need to be adjusted, but should not exceed 1 mg/kg.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Anti-estrogenic activity, anabolic effects, negative feedback on gonadotropin release | 0.5 mg/kg | PO | once daily | — | 🌎 NA |
- Anti-estrogenic activity, anabolic effects, negative feedback on gonadotropin release: Dose may need to be adjusted, but should not exceed 1 mg/kg. Use is highly controversial due to hepatotoxicity.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Methyltestosterone is a synthetic androgenic and anabolic steroid hormone. It is a 17-alpha-alkylated derivative of testosterone, which significantly reduces its first-pass hepatic metabolism, allowing for effective oral administration.
In veterinary medicine, it is primarily utilized for:
- Hormone-responsive dermatoses: Particularly Alopecia X (hair cycle arrest) in dogs, when melatonin therapy has failed.
- Reproductive management: Suppression of estrus or treatment of pseudopregnancy in female dogs.
- Hormone-dependent tumors: Adjunctive treatment for certain estrogen-dependent mammary tumors.
Clinical Pearl: Its use in veterinary medicine, particularly in cats, is highly controversial and generally discouraged due to a significant risk of severe hepatotoxicity. Cats appear to be uniquely susceptible to hepatic injury from 17-alpha-alkylated androgens.
Mechanism of action
Methyltestosterone acts as an exogenous androgen, binding to intracellular androgen receptors (AR) in target tissues.
- Mechanism: Free methyltestosterone enters cells → binds to cytosolic AR → the receptor-ligand complex translocates to the nucleus → binds to specific DNA sequences (androgen response elements) → modulates gene transcription.
- Anabolic Effects: Stimulates erythropoiesis (increases red blood cell production), enhances nitrogen balance, promotes protein anabolism (requires adequate caloric and protein intake), and increases retention of potassium, sodium, and phosphorus.
- Pharmacokinetic Advantage: The addition of a methyl group at the C-17 alpha position sterically hinders hepatic degradation, providing higher oral bioavailability compared to native testosterone.
Safety & warnings
Contraindications
- Hepatic dysfunction or pre-existing liver disease
- Pregnancy (Category X - causes fetal masculinization)
- Prostate cancer or severe prostatic hypertrophy
Adverse effects
- Hepatotoxicity (elevated liver enzymes, icterus, periportal hepatocyte enlargement)
- Virilization of females (clitoral hypertrophy, vaginitis)
- Vaginal discharge
- Prostatic hyperplasia in males
- Increased aggression or behavioral changes
- Seborrhea
- Premature epiphyseal closure in young animals
Precautions
Important Precautions
- Hepatotoxicity: Chronic use is strongly associated with liver damage. Baseline and serial liver enzyme monitoring is mandatory.
- Cardiac Disease: Use with extreme caution in patients with heart failure due to the potential for sodium and water retention.
- Growing Animals: Prolonged use in young, growing animals can cause premature epiphyseal closure, stunting growth.
- Laboratory Interference: Can decrease thyroxine-binding globulin, leading to decreased total T4 levels (free T4 remains unaffected).
Drug interactions
Methyltestosterone may increase serum cyclosporine levels, potentially leading to toxicity.
Methyltestosterone may decrease serum glucose levels, reducing insulin requirements.
May decrease serum glucose levels, increasing the risk of hypoglycemia.
Methyltestosterone may increase anticoagulant effects, increasing bleeding risk.
Monitoring
- Baseline and serial hepatic function panels (ALT, AST, ALP, Bilirubin)
- Clinical signs of hepatotoxicity (icterus, anorexia, weight loss, vomiting)
- Behavioral changes (aggression)
- Prostatic evaluation in intact males
Pharmacokinetics
Absorption
Absorbed from the GI tract and oral mucosa. Undergoes significantly less first-pass hepatic metabolism than orally administered native testosterone due to 17-alpha alkylation.
Distribution
Highly protein-bound in plasma, primarily to sex hormone-binding globulin (SHBG) and albumin.
Metabolism
Metabolized in the liver. In dogs, principle metabolites found in urine are glucuronidated forms (both conjugated and free) of methyltestosterone. Unlike humans, sulfated forms are not a major metabolic component.
Elimination
Excreted primarily in the urine as conjugated metabolites.
Overdose
Information on acute toxicity in veterinary species is limited.
- Acute signs: Nausea, vomiting, and edema are the most likely effects of a single massive overdose.
- Management: Consider gastrointestinal decontamination if ingestion is recent. Monitor liver function closely with large overdoses and provide supportive care.
Available products
Formulations
- Oral tablets
- Buccal tablets
- Oral capsules
Human-labeled
- Methyltestosterone Tablets: 10 mg & 25 mg (Methitest, generic)
- Methyltestosterone Buccal Tablets: 10 mg (generic)
- Methyltestosterone Capsules: 10 mg (Testred, Android, Virilon)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store tablets or capsules below 40°C, preferably between 15°-30°C (59°-86°F) in well-closed containers, unless otherwise specified by the manufacturer.
Client information
Important Information for Pet Owners
- Purpose: This medication is a hormone used to treat specific hair loss conditions (like Alopecia X) or to manage certain reproductive issues.
- Liver Risks: The most serious side effect is liver damage. Blood tests are required before starting this medication and regularly during treatment to ensure your pet's liver is handling it well.
- Behavioral Changes: Watch for increased aggression or changes in your pet's normal behavior.
- Physical Changes: Female dogs may develop male-like physical traits or vaginal discharge. Male dogs may develop prostate issues.
- When to Call the Vet: Stop the medication and contact your veterinarian immediately if your pet stops eating, starts vomiting, loses weight rapidly, or if you notice a yellowing of the eyes, gums, or skin (jaundice).
- Human Safety: Pregnant women should avoid handling this medication, as it can cause severe birth defects.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.