Anabolic steroidAndrogen19-nortestosteroneOralDesigner steroidProgestin

Tetrahydrogestrinone

Also known as THG · The Clear

Written by enwyReviewed 15 Jul 20261 sources0 comments

The 'Clear' at the centre of the BALCO doping scandal — a non-esterified oral progestin-derived steroid engineered to be undetectable until anti-doping chemists reverse-engineered it in 2003. Potent androgen and progesterone receptor activity in vitro, but no legitimate human trials.

01 Overview

Tetrahydrogestrinone (THG) is a hydrogenated analogue of gestrinone/trenbolone, developed clandestinely and supplied to elite athletes by the Bay Area Laboratory Co-operative (BALCO). It was designed specifically to evade mass-spectrometry screening and had no medical or commercial use.

After a used syringe was submitted to anti-doping authorities, chemists identified the structure and rapidly built a detection assay. In vitro work confirmed strong binding to androgen and progesterone receptors. Beyond seized material and athlete testimony, there is no published human pharmacology.

02 Mechanism

Potent agonist at the androgen receptor with additional progesterone-receptor activity; its trenbolone-like 19-nor structure drives strong anabolic signalling without aromatisation to estrogen.

03 Dosing

Tier	Dose	Route	Notes
Anecdotal	1–5 mg	Sublingual	Reportedly dosed as sublingual drops; no validated regimen.

Ester comparison

Ester	Half-life	Injection freq.	Testosterone by mass

04 Effects

Effect	Magnitude	Evidence
Anabolic / performance effectUsed by athletes for performance gains; effect size never measured under controlled conditions.	unquantified	Anecdotal
High AR and PR bindingIn vitro assays show potent androgen- and progesterone-receptor activation.	strong in vitro affinity	Preclinical

05 Side effects

Effect	Severity	Frequency	Evidence	Countermeasures
HPTA suppressionStrong suppression of endogenous testosterone anticipated from potent androgen/progestin activity.	Severe	Expected	Preclinical
Progestogenic effectsProgesterone-receptor activity may contribute to gynecomastia and libido changes.	Moderate	Uncertain	Preclinical

06 Legal status

United States

Schedule III anabolic steroid

Added to the controlled anabolic steroid list after the BALCO case. · as of Jan 2026

07 References

Tetrahydrogestrinone: discovery, synthesis, and detection in urineRapid Communications in Mass Spectrometry, 2004

08 Discussion0 comments

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This page is reference information, not medical advice. Doses and protocols are documented as they appear in the clinical literature and in practice — describing them is not a recommendation to use them. Countermeasures listed here are not a substitute for a physician. Legal status varies by jurisdiction and changes.