Tetrahydrogestrinone; 13β,17α-diethyl-17β-hydroxy-4,9,11-estratrien-3-one; The Clear (Victor Conte of BALCO Labs) is 18-homologated & 17α-ethylated gestrinone & a Δ4,9,11 (triene). Bill Llewellyn wrote a great article about this in Muscular Development magazine after the news of this drug & the BALCO Labs conspiracy came to light.
It's a surprisingly weak AR ligand (AR relative transactivation potency is < 25% DHT's). Instead, it exerts its potent effects primarily by modulating glucocorticoids (e.g., decreasing GR #, suppressing GREs in genes like tyrosin aminotransferase).
So, potently hepatotoxic and progestagenic, its efficacy/tolerability would fare worse than i.m. trenbolone certainly, and its use was mostly justified by its (for a time) undetectability by doping authorities, being so unusual in its synthesis, structure, metabolism.