Hair loss does not occur very often. The most common side effect is low function of the normal pituitary gland. This can occur up to 1 year or many years after treatment. One study showed that 50% of patients developed one or more pituitary hormone deficiencies within 2 years of conventional radiation therapy. Gamma Knife focused radiation studies show that approximately 1/3 of patients will develop one pituitary hormone deficiency, and it is estimated that the percentage will increase as the time after treatment increases. The development of pituitary hormone deficiency is not desired, however hormone replacement therapy is effective. An uncommon side effect is visual impairment. These risks must be weighed against the risk of tumor regrowth.