Arimistane

Overview

Arimistane is a non-peptide C19 steroidal compound (androstane-based) marketed as a mechanism-based aromatase inhibitor and sold as a gray-market bodybuilding supplement ingredient. It is a 7-keto-DHEA metabolite/degradation product with no approved therapeutic use. The FDA determined in 2021 that arimistane does not meet the definition of a dietary ingredient and fails GRAS criteria for food use. It is prohibited under the WADA Prohibited List (Section S4, Aromatase Inhibitors) and was added to the list in 2017.

Mechanism of Action

Arimistane is a C19 steroid bearing 7,17-diketone groups on an androsta-3,5-diene core, marketed as a mechanism-based ("suicide") irreversible aromatase inhibitor. Direct enzyme-kinetics data (Ki, kinact) specifically for arimistane were not found in primary literature; the closest sourced data are for near-neighbor steroids: androst-5-ene-7,17-dione (differing only in lacking the 3,4-double bond) acts as a time-dependent, NADPH-dependent suicide substrate of human placental aromatase in vitro (Ki ~0.14–35 µM, kinact ~0.036–0.19/min), and a series of androsta-3,5-dien-7-ones/androst-5-en-7-ones competitively inhibited aromatase with Ki 0.058–45 µM (17-oxo forms more potent than 17-beta-ols). These class data support the aromatase-inhibitor assignment but do not confirm kinetics for arimistane itself.

Research Summary

No registered efficacy or safety clinical trials exist for arimistane. The only human data are two small anti-doping analytical studies: (1) a single 25 mg oral dose in 3 healthy volunteers produced up to 15 novel urinary metabolites, with parent compound detected in the sulfate fraction and no relevant acute effects on the steroid profile; (2) a separate single-dose study (3 volunteers, up to 10 hours) identified 12 additional reduced/hydroxylated urinary metabolites and detected unchanged parent in urine. In vitro (human placental microsomes): the close analog androst-5-ene-7,17-dione is a time-dependent, NADPH-dependent suicide substrate of aromatase; a series of related androsta-3,5-dien-7-ones/androst-5-en-7-ones competitively inhibited aromatase (Ki 0.058–45 µM), with 17-oxo derivatives more potent than 17-beta-hydroxy derivatives. Arimistane itself was not unambiguously confirmed among the specific tested compounds in the latter study.

Reported Side Effects

• No controlled human safety data; class-level concern for estrogen suppression with reciprocal androgen rise
• Prohibited under WADA Section S4 (Aromatase Inhibitors); added 2017
• FDA determined it does not meet GRAS criteria and is not a lawful dietary ingredient
• Analytically identified as undeclared designer steroid in commercial supplements
• Vendor-claimed liver/kidney/behavioral effects not corroborated in primary literature

Compare Arimistane with Others

Research References

• Androsta-3,5-diene-7,17-dione, PubChem Compound Summary for CID 150910.
• Identification of the designer steroid Androsta-3,5-diene-7,17-dione in a dietary supplement. 2019. PMID 30892803.
• Detection of urinary metabolites of arimistane in humans by gas chromatography coupled to high accuracy mass spectrometry for antidoping analyses. 2019. PMID 31295379.
• Detection of urinary arimistane metabolites in humans by liquid chromatography-mass spectrometry. 2021. PMID 33713366.

Frequently asked questions

How does Arimistane work?

Arimistane is a C19 steroid bearing 7,17-diketone groups on an androsta-3,5-diene core, marketed as a mechanism-based ("suicide") irreversible aromatase inhibitor. Direct enzyme-kinetics data (Ki, kinact) specifically for arimistane were not found in primary literature; the closest sourced data are for near-neighbor steroids: androst-5-ene-7,17-dione (differing only in lacking the 3,4-double bond) acts as a time-dependent, NADPH-dependent suicide substrate of human placental aromatase in vitro (Ki ~0.14–35 µM, kinact ~0.036–0.19/min), and a series of androsta-3,5-dien-7-ones/androst-5-en-7-ones competitively inhibited aromatase with Ki 0.058–45 µM (17-oxo forms more potent than 17-beta-ols). These class data support the aromatase-inhibitor assignment but do not confirm kinetics for arimistane itself.

What does the research say about Arimistane?

No registered efficacy or safety clinical trials exist for arimistane. The only human data are two small anti-doping analytical studies: (1) a single 25 mg oral dose in 3 healthy volunteers produced up to 15 novel urinary metabolites, with parent compound detected in the sulfate fraction and no relevant acute effects on the steroid profile; (2) a separate single-dose study (3 volunteers, up to 10 hours) identified 12 additional reduced/hydroxylated urinary metabolites and detected unchanged parent in urine. In vitro (human placental microsomes): the close analog androst-5-ene-7,17-dione is a time-dependent, NADPH-dependent suicide substrate of aromatase; a series of related androsta-3,5-dien-7-ones/androst-5-en-7-ones competitively inhibited aromatase (Ki 0.058–45 µM), with 17-oxo derivatives more potent than 17-beta-hydroxy derivatives. Arimistane itself was not unambiguously confirmed among the specific tested compounds in the latter study.