Half-life is the term that describes the time taken for your testosterone levels to drop in half following administration. A period of 8 days means that in that time, your testosterone level would drop in half; this will continue every eight days until the Testosterone is eliminated from your system. You would eliminate a substance with a low half-life from the system faster than a substance with a high half-life, which will take longer to stop. Hence, many users prefer products like testosterone cypionate because of its long half-life.