Testosterone Support + Anti Estrogen. Muscle. Libido. Strength. Performance. Powerful Multi-Phase Test Booster for Muscle, Libido, Strength and Performance! ISA-TEST GF is high performance testosterone booster comprised of a precise combination of natural ingredients clinically shown to cause increases in testosterone and a reduction in the “female-hormone” estrogen. ISA-TEST GF is designed to promote noticeable gains in strength, increased muscle mass, and improved sexual drive and performance.