19 Nor DHEA is the prohormone of choice for many people looking to improve their overall lean muscle mass. Prohormones are substances that get converted into hormones in the body that amplify the effects of the steroids already in your body. Prohormones like 19-Nor are the most powerful type of supplement you could take if you’re looking to increase testosterone and build muscle mass. Prohormones have been shown to cause great gains in strength and size, so you’ll feel stronger and have more endurance.