Another way that steroids are used is something called stacking. In stacking you use various types of these substances that are similar to testosterone known as anabolic steroids to try to achieve a similar effect and you might stack on a cycle. These type of high-dose products have the impact of increasing testosterone in the blood, which can lead to a muscle growth and some useful things, but at the same time, they send a message to the testicle, “Stop producing testosterone. We’ve got plenty in our bloodstream so shut down.” As part of that same process, those stem cells, the spermatogonia that are making sperms, are also told, “Slow down or stop”. And sometimes if you do a high enough dose for long enough, those cells never get the message that they are supposed to restart.