My older brother used to be into competitive body building. He got involved with steroids. Probably not shocking, I know. I think you really shouldn’t alter your body with chemicals to gain muscle mass. But, to each their own, right? He had used estrogen blockers and had side effects along with them.
He stopped taking steroids and estrogen blockers after a while and started getting out of the competition circuit. The side effects he had with the estrogen blockers were mostly fatigue and headaches. Those went away after he stopped using them. He seems to be back to normal these days.