There is a complicated network of hormones involved in the male reproductive system and, in some men, the signals from their brains to their testes don't work quite right. Underlying causes of hormonal imbalance can include abnormalities of the hypothalamus, pituitary, thyroid, or adrenal glands. Problems in the testicles can also be a factor. Injectable or pill-form hormones are often used to treat hormone-related fertility issues. Overall, hormone therapy is among the most successful treatments for male infertility.