Danazol is an oral synthetic steroid derived from ethisterone (17α-ethynyltestosterone). It is a weak androgen that also suppresses the pituitary hormones LH and FSH. The FDA approved it in 1976 as Danocrine. Generic capsules are still sold in the US for two labeled uses: endometriosis and prevention of hereditary angioedema (HAE) attacks.

Off label, it has been studied in immune thrombocytopenia, bone marrow failure caused by short telomeres, and male breast enlargement (gynecomastia). Despite sometimes being grouped with “estrogen control” drugs, danazol is not an aromatase inhibitor or a SERM. It lowers estrogen mainly by shutting down ovarian hormone production, and it does not bind the estrogen receptor.

This page summarizes what the FDA label, clinical trials and guidelines report. It is for education only and is not medical advice.

Property	Detail
Drug class	Synthetic steroid (ethisterone derivative); weak androgen and antigonadotropin
Brand / approval	Danocrine (Sanofi), NDA 017557, approved 1976, now discontinued; generic capsules remain
Route	Oral capsule
Strengths	50 mg, 100 mg, 200 mg
Labeled doses	Endometriosis 200–800 mg/day in 2 doses; HAE 200 mg 2–3 times daily, then tapered
Half-life (label)	9.7 h after a single 400 mg dose in men; 23.7 h after 6 months of 200 mg three times daily
Food effect	A high-fat meal raises exposure about 3–4 fold
Estrogen receptor	Does not bind it
US status	Prescription only; not named as a Schedule III anabolic steroid in 21 CFR 1308.13
WADA status	Prohibited at all times (S1.1 anabolic androgenic steroids)

What it is

The label describes danazol as 17α-pregna-2,4-dien-20-yno[2,3-d]isoxazol-17-ol, formula C₂₂H₂₇NO₂, molecular weight 337.46 g/mol (FDA label; PubChem). Two structural features set it apart from testosterone:

Feature	What it means
Isoxazole ring fused to the A-ring	A small ring containing nitrogen and oxygen sits where testosterone has its 3-keto group.
17α-ethynyl group	Inherited from ethisterone, the parent compound. Danazol is taken by mouth.

Early descriptions called danazol a “selective antigonadotrophin.” A 1981 review of its pharmacology argued that this label was wrong, because the drug has many separate actions (Barbieri and Ryan, Am J Obstet Gynecol 1981). Danazol:

blocks the midcycle LH and FSH surge;
binds androgen, progesterone and glucocorticoid receptors, but not estrogen receptors;
binds sex hormone-binding globulin (SHBG) and corticosteroid-binding globulin;
inhibits several enzymes of steroid hormone production;
has hormonally active metabolites.

Effect on SHBG and free testosterone

Danazol lowers SHBG, the protein that carries testosterone in blood, and also displaces testosterone from it. In 25 women with endometriosis given 50–600 mg/day for 6 months, the fall in SHBG and the rise in the free share of testosterone were dose-related (Forbes et al., Clin Endocrinol 1986). Free testosterone doubled in the first week, then settled at 25–50% above pretreatment levels. Total testosterone fell. This free-androgen effect helps explain why danazol causes androgenic side effects even though its own receptor activity is weak.

Pharmacokinetics

From the current generic label (FDA label), after a single 400 mg dose in 15 healthy men:

Parameter	Mean ± SD
Peak concentration (Cmax)	69.6 ± 29.9 ng/mL
Time to peak (Tmax)	2.47 ± 1.62 h
Total exposure (AUC)	601 ± 181 ng·h/mL
Elimination half-life	9.70 ± 3.29 h

Key points from the label:

Half-life varies. It was 9.7 h after one dose in men, but 23.7 h after 6 months of 200 mg three times daily in women with endometriosis. Steady state is reached after about 6 days of twice-daily dosing.
Absorption does not scale with dose. In fasting women, a 4-fold higher dose raised exposure only 1.6-fold (2.5-fold when fed).
Food matters a lot. A meal with more than 30 g of fat raised exposure and peak levels about 3–4 fold. With ordinary meals, a 2–2.5 fold difference between fed and fasted dosing remained.
Metabolism. The two main urinary metabolites are 2-hydroxymethyl danazol and ethisterone. At least ten other products appear in feces.

Danazol can also interfere with lab tests for testosterone, androstenedione and DHEA, and it lowers thyroid-binding globulin and total T4 without changing TSH.

Approved medical use

Current US generic labels list two indications (FDA label):

Indication	Labeled dose
Endometriosis, moderate to severe or with infertility	800 mg/day in 2 divided doses, then titrated down; 3–6 months, up to 9
Endometriosis, mild	200–400 mg/day in 2 divided doses
Hereditary angioedema (prevention of attacks)	200 mg 2–3 times daily, then reduced by 50% or less every 1–3 months to the lowest effective dose

For endometriosis, therapy starts during menstruation or after a negative pregnancy test. Ovulation and periods usually return 60–90 days after stopping.

The older Danocrine label also listed fibrocystic breast disease at 100–400 mg/day (Danocrine label, 2011). That label noted that about 50% of patients may have symptoms return within a year. This indication does not appear on current generic labels.

What the research shows

Endometriosis

A Cochrane review found five placebo-controlled randomized trials (Selak et al., Cochrane 2007). Danazol, alone or after surgery, relieved endometriosis pain better than placebo and improved laparoscopic scores. The benefit was still present six months after stopping. The reviewers concluded that androgenic side effects limit its use.

Hereditary angioedema

HAE is a genetic deficiency of C1 esterase inhibitor (C1-INH) that causes attacks of swelling, including in the airway. Danazol raises the missing protein.

In a double-blind crossover trial in 9 patients (Gelfand et al., NEJM 1976):

Measure	Placebo	Danazol
Courses ending in an attack	44 of 47	1 of 46
C1 esterase inhibitor level	—	Rose 3–4 fold
Complement C4 level	—	Rose about 15 fold

The biochemical changes began on day 1, peaked within 1–2 weeks, and fell quickly after stopping.

A long-term survey of 118 German and Danish patients treated for 2 months to 30 years found (Bork et al., Ann Allergy Asthma Immunol 2008):

111 of 118 patients responded;
54 (45.8%) became symptom free or had at most 1 attack a year;
attack frequency fell to 16.2% of the pretreatment rate;
adverse effects occurred in 93 of 118, and led 30 patients to stop.

The reported adverse effects included weight gain, virilization, menstrual changes, headache, depression and liver adenomas. The 2021 WAO/EAACI guideline now recommends androgens such as danazol only as second-line long-term prevention, because of their adverse effects, drug interactions and contraindications (Maurer et al., WAO J 2022). It advises against danazol doses above 200 mg/day for long periods, against use in children before full puberty (Tanner stage V), and against use for treating an attack once it has started.

Immune thrombocytopenia (off label)

In immune thrombocytopenia (ITP), antibodies destroy platelets. An early case series treated 22 patients, all on glucocorticoids and 15 after spleen removal (Ahn et al., NEJM 1983). Fifteen benefited and 11 had sustained normal platelet counts, with remissions lasting 2–13 months.

A later randomized, open-label phase 2 trial in 93 adults with steroid-resistant or relapsed ITP compared danazol 200 mg twice daily for 16 weeks with or without all-trans retinoic acid (ATRA) (Feng et al., Lancet Haematol 2017):

Arm	Sustained response at 12 months
Danazol alone	12 of 48 (25%)
Danazol + ATRA	28 of 45 (62%)

The odds ratio was 4.94 (95% CI 2.03–12.02). One patient on danazol alone had grade 3 liver injury.

Telomere diseases (off label)

Inherited defects in telomere repair cause bone marrow failure, lung fibrosis and liver disease. An NIH phase 1–2 study gave 27 patients danazol 800 mg/day for 24 months (Townsley et al., NEJM 2016). It was stopped early because the drug was working:

Outcome	Result
Slower telomere loss (primary end point, intention to treat)	12 of 27 (44%; 95% CI 26–64)
Telomere gain at 24 months	11 of 12 evaluable; mean +386 base pairs (95% CI 178–593)
Blood count response at 3 months	19 of 24 (79%)
Blood count response at 24 months	10 of 12 (83%)

The most common adverse events were raised liver enzymes (41%), muscle cramps (33%), edema (26%) and lipid abnormalities (26%). This was a single-arm study with no placebo group.

Gynecomastia (off label)

Evidence for danazol in male breast enlargement is limited to two small studies:

Randomized trial. 55 men with idiopathic gynecomastia received danazol 200 mg twice daily or placebo for 3 months (Jones et al., Ann R Coll Surg Engl 1990). Danazol improved tenderness and measured breast size more than placebo. Surgery was still planned for 27% of the danazol group vs 50% of the placebo group. Significant weight gain occurred only on danazol.
Retrospective comparison. In a Hong Kong breast clinic, complete resolution occurred in 8 of 20 men (40%) on danazol 400 mg/day vs 18 of 23 (78%) on tamoxifen 20 mg/day (Ting et al., Am Surg 2000). Relapse occurred only in the tamoxifen group (5 men).

Neither study was large or long. For context on the main alternative, see tamoxifen.

Athletic performance

We found no controlled human studies of danazol on muscle, strength or endurance. The label notes that danazol can raise red cell counts and cause reversible polycythemia (too many red cells), but this has not been studied as a performance effect.

Side effects and risks

The current label has no boxed warning, but its warnings section is serious (FDA label).

Pregnancy

Danazol is contraindicated in pregnancy. Exposure in the womb has caused masculinization of female fetuses, including clitoral enlargement, labial fusion and ambiguous genitalia. The label recommends a sensitive pregnancy test before starting and non-hormonal contraception during treatment.

Blood clots and stroke

The label reports thrombotic events, including sagittal sinus thrombosis (a clot in a large brain vein) and life-threatening or fatal strokes. Active or past thromboembolic disease is a contraindication. In 17 HAE patients on danazol for at least 2 years, markers of clotting activation were higher than in matched controls: prothrombin fragments 286 vs 164 pmol/L (p = 0.002) (Birjmohun et al., Clin Ther 2008).

Liver

Danazol is linked to several kinds of liver harm:

Enzyme rises and jaundice, reported at 400 mg/day or more and usually reversible.
Peliosis hepatis (blood-filled cysts) and benign liver adenomas with long-term use. Both can stay silent until they bleed into the abdomen.
Rare serious injury: cholestatic jaundice, liver failure and, after long-term use, malignant liver tumors.

Case reports describe hepatocellular carcinoma in people taking danazol for HAE, including in livers without cirrhosis (Berkel et al., Neth J Med 2014). On the other hand, a 5-year follow-up of 46 HAE patients on low-dose danazol vs 46 not on it found no clinically relevant difference in liver tests and no tumors on ultrasound (Farkas et al., Eur J Clin Pharmacol 2010). Dose and duration appear to matter, and the label calls for periodic liver tests.

Intracranial hypertension

Danazol has been associated with benign intracranial hypertension (pseudotumor cerebri), a rise in pressure around the brain. Early signs include headache, nausea, vomiting, visual disturbance and swelling of the optic disc. The label says to stop the drug if these appear.

Lipids

The label warns that HDL (“good” cholesterol) can fall and LDL may rise, sometimes markedly. In a randomized crossover trial in 15 healthy men, 200 mg/day for 4 weeks lowered HDL by 23% and apolipoprotein A-I by 21% (Birjmohun et al., Clin Ther 2008). In the same paper, long-term HAE patients on about 170 mg/day did not differ from controls in HDL or carotid wall thickness.

Androgenic and other effects

From the label:

Androgenic: weight gain, acne, oily skin, mild hirsutism, hair loss and voice changes. Voice deepening may persist after stopping. Clitoral enlargement is rare.
Low-estrogen effects: flushing, sweating, vaginal dryness and smaller breast size.
Menstrual: spotting, irregular cycles and amenorrhea; prolonged amenorrhea after stopping has occasionally been reported.
Men: a modest fall in sperm production; long-term use may affect semen volume, sperm count and motility.
Metabolic: insulin resistance, fluid retention and raised blood pressure.

Interactions

The label lists these interactions:

Drug	Effect with danazol
Warfarin	Prolonged prothrombin time
Carbamazepine	Higher carbamazepine levels
Cyclosporine, tacrolimus	Higher levels and more kidney toxicity
Simvastatin, atorvastatin, lovastatin	Higher risk of myopathy and rhabdomyolysis
Insulin and other diabetes drugs	Insulin resistance; higher insulin needs
Vitamin D analogs (hypoparathyroidism)	Stronger rise in calcium

Who should not take it

Label contraindications:

pregnancy or breastfeeding;
undiagnosed abnormal genital bleeding;
markedly impaired liver, kidney or heart function;
porphyria;
androgen-dependent tumors;
active or past thrombosis or thromboembolic disease;
hypersensitivity to danazol.

Legal status and use outside medicine

In the US, danazol is a prescription drug. It is not among the anabolic steroids named in the DEA’s Schedule III list (21 CFR 1308.13). The brand Danocrine is listed as discontinued, while generic capsules from several manufacturers remain approved (Drugs@FDA, NDA 017557).

In sport, WADA names danazol among the anabolic androgenic steroids in class S1.1. It is prohibited at all times, in and out of competition (WADA 2026 Prohibited List).

Key takeaways

A weak androgen with many actions. Danazol suppresses LH and FSH, blocks ovarian hormone production, binds androgen and progesterone receptors, and raises free testosterone by lowering SHBG.
Not an estrogen blocker in the usual sense. It does not bind the estrogen receptor and is not an aromatase inhibitor. It lowers estrogen mainly by suppressing the ovaries.
Two labeled uses remain. Endometriosis (up to 800 mg/day) and HAE prevention (starting at 200 mg 2–3 times daily). Guidelines now rank it second line for HAE.
Interesting off-label data. Small trials show benefit in ITP and in telomere-related marrow failure. Evidence in gynecomastia is limited to one small RCT and one retrospective study.
Serious risks. It is contraindicated in pregnancy and carries warnings for clots and stroke, liver tumors and peliosis, intracranial hypertension and lower HDL.
Banned in sport. WADA prohibits it at all times as an anabolic steroid.

Sources

Teva Pharmaceuticals USA. Danazol capsules, USP, prescribing information. Rev. 10/2022. DailyMed.
Sanofi-Aventis U.S. Danocrine (danazol capsules, USP) prescribing information, NDA 017557, 2011. FDA; Drugs@FDA, NDA 017557.
National Center for Biotechnology Information. Danazol, PubChem CID 28417. PubChem.
Barbieri RL, Ryan KJ. Danazol: endocrine pharmacology and therapeutic applications. Am J Obstet Gynecol. 1981;141(4):453–463. PubMed.
Forbes KL, Dowsett M, Rose GL, Mudge JE, Jeffcoate SL. Dosage-related effects of danazol on sex hormone binding globulin and free and total androgen levels. Clin Endocrinol (Oxf). 1986;25(5):597–605. PubMed.
Selak V, Farquhar C, Prentice A, Singla A. Danazol for pelvic pain associated with endometriosis. Cochrane Database Syst Rev. 2007;(4):CD000068. PubMed.
Gelfand JA, Sherins RJ, Alling DW, Frank MM. Treatment of hereditary angioedema with danazol. Reversal of clinical and biochemical abnormalities. N Engl J Med. 1976;295(26):1444–1448. PubMed.
Bork K, Bygum A, Hardt J. Benefits and risks of danazol in hereditary angioedema: a long-term survey of 118 patients. Ann Allergy Asthma Immunol. 2008;100(2):153–161. PubMed.
Maurer M, Magerl M, Betschel S, et al. The international WAO/EAACI guideline for the management of hereditary angioedema - The 2021 revision and update. World Allergy Organ J. 2022;15(3):100627. PMC.
Ahn YS, Harrington WJ, Simon SR, et al. Danazol for the treatment of idiopathic thrombocytopenic purpura. N Engl J Med. 1983;308(23):1396–1399. PubMed.
Feng FE, Feng R, Wang M, et al. Oral all-trans retinoic acid plus danazol versus danazol as second-line treatment in adults with primary immune thrombocytopenia: a multicentre, randomised, open-label, phase 2 trial. Lancet Haematol. 2017;4(10):e487–e496. PubMed.
Townsley DM, Dumitriu B, Liu D, et al. Danazol treatment for telomere diseases. N Engl J Med. 2016;374(20):1922–1931. PubMed.
Jones DJ, Holt SD, Surtees P, et al. A comparison of danazol and placebo in the treatment of adult idiopathic gynaecomastia: results of a prospective study in 55 patients. Ann R Coll Surg Engl. 1990;72(5):296–298. PubMed.
Ting AC, Chow LW, Leung YF. Comparison of tamoxifen with danazol in the management of idiopathic gynecomastia. Am Surg. 2000;66(1):38–40. PubMed.
Birjmohun RS, Hovingh GK, Stroes ES, et al. Effects of short-term and long-term danazol treatment on lipoproteins, coagulation, and progression of atherosclerosis: two clinical trials in healthy volunteers and patients with hereditary angioedema. Clin Ther. 2008;30(12):2314–2323. PubMed.
Farkas H, Czaller I, Csuka D, et al. The effect of long-term danazol prophylaxis on liver function in hereditary angioedema-a longitudinal study. Eur J Clin Pharmacol. 2010;66(4):419–426. PubMed.
Berkel AE, Bouman DE, Schaafsma MR, Verhoef C, Klaase JM. Hepatocellular carcinoma after danazol treatment for hereditary angio-oedema. Neth J Med. 2014;72(7):380–382. PubMed.
World Anti-Doping Agency. The 2026 Prohibited List. WADA 2026 Prohibited List.
US Drug Enforcement Administration. Schedules of controlled substances: Schedule III. 21 CFR 1308.13. 21 CFR 1308.13.

Danazol