Creatine is an amino acid made in the liver and stored in muscles. When combined with phosphate, it is a readily available source of energy in the body. In the diet, creatine is found in milk, red meat, and some fish.

Medicinal Claims: People take supplements of creatine to improve physical or athletic performance and to decrease fatigue. Its use is associated with weight gain. A few studies indicate that creatine can increase the amount of work performed with a short maximal effort (for example, in sprinting). However, a few others indicate no improvement in this type of activity.

Possible Side Effects: Creatine supplements may elevate levels of creatine in the urine and blood and cause kidney dysfunction. People who have diabetes or a history of kidney dysfunction or who take drugs that are toxic to the kidneys should avoid creatine supplements.

Last full review/revision February 2009 by Ara DerMarderosian, PhD