Doesn't know how steroids work and how to mask them? OK, the body produces natural testosterone and natural epistosterone and they both balance the body and close in ratio like T 1.15:E 1. Some athletes have higher levels of T around 3.5, so when they decide that they want to get stronger and faster and so forth, they use anabolic steroids to increase their T level up to 15 or even more. The urine or blood test will show that in relation to the E level, so they use diuretics or epistosterone to make the levels close to normal. In the process, however, when they first take the masking agent, it will make their T level so low and slowly will go back up until the time for testing. So, when you get tested by surprise, your T level will look very low next to the E levels.