Arginine is considered a semi-essential amino acid, as it does not fall perfectly in the essential or nonessential categories. Arginine can be synthesized in the body at adequate levels for maintenance in adults. It may not, however, be produced quickly enough during periods of growth, and is considered essential at those times. Arginine stimulates certain glands, particularly the thymus and the pituitary. Because the pituitary secretes growth hormone, arginine is required for normal growth. And because of this participation in growth, it has become very popular for its muscle-building and fat-burning effects among athletes. Other functions of this amino acid are its ability to aid in liver detoxification, maintain immune function, boost sperm count, and assist in conditions involving kidney impairment. It also causes retardation of tumors and cancer. Arginine is thought to be beneficial in the treatment of cirrhosis of the liver and other liver problems. Its high content in scar tissue points to its involvement in tissue repair and collagen production. It also contributes to increases in muscle mass and decreases in body fat. Pregnant and lactating women should avoid taking arginine because of its involvement in growth and shedding of fat. Since arginine is required for the herpes virus to replicate, reducing arginine in the diet appears to lessen the normal growth of herpes.