Can testosterone supplements affect male fertility?

Every guy's brain is equipped with a tiny testosterone "thermostat" that constantly monitors the level of this key hormone in his blood. When levels fall, the brain sends signals to the testicles to boost production, and when levels rise, signals tell the testicles to shut down. Adding extra testosterone by taking supplements tricks the brain. Sensing the high levels, the brain shuts down testosterone production and sperm production, both of which happen in the testicles. As a result, the testicles shrink, soften, and the man's fertility plummets. He may still have normal erections and orgasms, so he probably won't realize anything's wrong, but he'll be shooting blanks.