AI’s are also sometimes used during PCT because of their ability to stimulate LH and FSH. However, they also lower estrogen levels and often too much during this phase. Part of the PCT plan is to allow the body to normalize and part of that is maintaining normal estrogen levels. Estrogen is not an evil hormone many men, especially steroid users often believe it is. Estrogen is extremely important for muscle building, sexual health, mental health and a host of other areas. Estrogen levels that are too high or too low, both can be very problematic.