Testosterone in a male may become deficient due to disease affecting either his pituitary gland (in the brain) or his testes. Older men may also suffer the effects of low testosterone due to the natural decline of testosterone with age (a.k.a. andropause). Common symptoms include breast formation, lack of morning erections, sexual thoughts, libido and poor erectile quality. Other men may also experience poor sleep patterns, weight gain, poorer mental concentration, mood swings, unexplained sweating and hot flushes.