Testolactone (Teslac) for First-Generation Aromatase Inhibition — Anabolic Steroids
First aromatase inhibitor. FDA-approved 1970 for breast cancer (withdrawn 2008). Weak potency. Historical significance. Superseded by modern AIs.
Overview
Testolactone (brand name Teslac) holds the distinction of being the first aromatase inhibitor approved by the FDA, receiving approval in 1970 for the treatment of advanced or metastatic breast cancer in postmenopausal women. Developed by Bristol-Myers Squibb, testolactone is a synthetic derivative of testosterone with a modified D-ring (delta-1-testololactone) that eliminates androgenic activity while conferring irreversible aromatase (CYP19A1) inhibition. However, by modern standards, testolactone is a remarkably weak aromatase inhibitor, achieving only approximately 20-30% suppression of systemic estrogen levels — far inferior to third-generation aromatase inhibitors such as anastrozole (Arimidex, >95% suppression), letrozole (Femara, >99% suppression), and exemestane (Aromasin, >95% suppression). The FDA withdrew approval of Teslac in 2008, not due to safety concerns, but because it had been completely superseded by the vastly more effective third-generation AIs. Testolactone was generally well-tolerated with a favorable side effect profile, primarily causing mild nausea, edema, and occasional maculopapular rash. It does not suppress the HPG axis and has no androgenic or estrogenic activity. In the context of anabolic steroid polypharmacy, testolactone was historically used as an estrogen management tool before the introduction of more potent AIs in the 1990s. Its weak aromatase inhibition made it insufficient for managing estrogen-related side effects (gynecomastia, water retention) of highly aromatizing AAS cycles. Today, testolactone is of primarily historical and pharmacological interest as the prototype aromatase inhibitor, and is very rarely used clinically or in performance-enhancement contexts due to the availability of far superior alternatives.
Indications
- FDA-approved (withdrawn 2008): Advanced breast cancer in postmenopausal women
- Historical: First aromatase inhibitor — prototype for drug class
- Historical: Estrogen management in AAS polypharmacy (before modern AIs)
- Off-label (historical): Precocious puberty in males
- Off-label (historical): Gynecomastia prevention (largely ineffective)
- Superseded by anastrozole, letrozole, and exemestane for all indications
Mechanism of Action
Testolactone administered orally at 250mg four times daily (1000mg total). Modified testosterone D-ring structure eliminates androgenic activity while maintaining oral bioavailability. Inconvenient dosing schedule contributed to its replacement
Dosing
| Compound | Dose | Frequency | Notes |
|---|---|---|---|
| Testolactone (Teslac) | 250 mg four times daily (1000 mg/day total) | Four times daily | Historical FDA-approved dose for breast cancer; product discontinued |
| Testolactone | 250 mg twice daily | Twice daily | Reduced dose used historically in AAS estrogen management (largely ineffective) |
Safety & Contraindications
- FDA approval WITHDRAWN in 2008 — superseded by modern aromatase inhibitors
- Weak aromatase inhibition (~20-30% estrogen suppression vs >95% for modern AIs)
- Insufficient for estrogen management in highly aromatizing AAS cycles
- Generally well-tolerated — mild nausea, edema, rash most common side effects
- No androgenic or estrogenic activity
- Does not suppress HPG axis at therapeutic doses
- No longer commercially available — discontinued product
- Drug of primarily historical significance
- Oral dosing: 250mg four times daily — inconvenient dosing schedule
- Rarely encountered in modern clinical or performance-enhancement settings