Androstenedione
Naturally occurring androgen/estrogen precursor produced by the adrenal glands, ovaries, and testes. Made famous by Mark McGwire's 1998 home-run season when he admitted using it as a supplement. Peak serum testosterone elevation is modest and transient (~3 hours). Banned by MLB in 2004 and classified Schedule III in the US in 2004.
Mechanism of Action
Rapidly converted in peripheral tissues by 17β-HSD to testosterone (primarily in males) and by aromatase to estrone. Peak testosterone elevation ~13% above baseline in most studies. Half-life is extremely short (~50 min). The short duration of action explains why RCTs show negligible long-term anabolic effect despite some acute testosterone elevation. More estrogen production (from aromatization) than testosterone relative to direct testosterone administration.
Typical Dosing
⚠ Warning Flags
- •Schedule III in the US (2004 Anabolic Steroid Control Act)
- •More estrogenic than anabolic in RCTs
- •Extremely short half-life renders it essentially ineffective
Effect Profile
Side Effect Profile
Research Studies
Effect of oral androstenedione on serum testosterone and adaptations to resistance training in young men
King DS, et al. · 1999
Gold-standard RCT: 8 weeks of androstenedione (300 mg/day) produced NO significant increase in serum testosterone, NO improvement in strength or lean mass versus placebo in resistance-training young men — definitively refuting its ergogenic claims.
Oral androstenedione administration and serum testosterone concentrations in young men
Leder BZ, et al. · 2000
Transient testosterone elevation (~13%) with rapid return to baseline; estradiol increases more substantially; no meaningful anabolic effect found, but estrogen-related side effects (elevated E2) documented.