Cardiac creatine levels are reported as depressed in chronic heart failure. Several studies report that creatine supplementation is associated with improved heart muscle strength, body weight and endurance in patients with heart failure. However, it is not clear what dose may be safe or effective. Supplementation is also reported to increase creatine in skeletal muscle in these patients, helping to increase strength and endurance. Well-designed studies comparing creatine with drugs used to treat heart failure are needed before a firm recommendation can be made. Heart failure should be treated by a qualified healthcare professional.

It has been suggested that creatine may help improve athletic performance or endurance by increasing time to fatigue (possibly by shortening muscle recovery periods). However, the results of research evaluating this claim are mixed. Findings from different studies disagree with each other, and most studies do not support the use of creatine to enhance sustained aerobic activities.

Multiple studies suggest that creatine may improve muscle mass and strength in men and women, particularly when accompanied by increased physical activity. However, studies of creatine in athletes have disagreed with each other. Although many experts believe that creatine may be useful for high-intensity, short-duration exercise, it has not been demonstrated effective in endurance sports. Benefit may be greatest when levels of creatine prior to supplementation are low, and in specific sub-populations such as older men.

Some individuals are born with a genetic disorder in which there is a deficiency of the enzyme guanidinoacetate methyltransferase (GAMT). A lack of this enzyme causes severe developmental delays and abnormal movement disorders. The condition is diagnosed by a lack of creatine in the brain. Although there is only limited research in this area.

There is early evidence that heart muscle may recover better and more rapidly after open-heart surgery if intravenous creatinine is administered during the operation. Further study is needed before a recommendation can be made.

There is limited research in this area, and results from different studies disagree with each other (with some trials noting reductions in total cholesterol and triglyceride levels). It remains unclear what effect creatine has on lipids. Additional studies are needed before a clear conclusion can be drawn.

There is preliminary evidence that creatine may be well-tolerated and safe in Huntington's disease patients. Further research is needed before a recommendation can be made.

Ornithine is a byproduct formed in the liver. Some individuals are born with a genetic disorder that prevents them from appropriately breaking down ornithine, and blood levels of ornithine become too high. High amounts of ornithine can lead to blindness, muscle weakness and reduced storage of creatine in muscles and the brain. Although there is only limited research in this area, early evidence suggests that long-term, daily creatine supplements may help replace missing creatine and slow vision loss.

In McArdle's disease, there is a deficiency of energy compounds stored in muscle. This leads to muscle fatigue, exercise intolerance, and pain when exercising. Creatine has been proposed as a possible therapy for this condition. However, research is limited, and the results of existing studies disagree with each other. Therefore, it remains unclear if creatine offers any benefits to patients with McArdle's disease.

Creatine loss is suspected to cause muscle weakness and breakdown in Duchenne muscular dystrophy. Further research of creatine supplementation for muscular dystrophy is needed before a recommendation can be made.

There is early evidence that intravenous creatine following a heart attack may be beneficial to heart muscle function, and may prevent ventricular arrhythmias. Further study is needed before a recommendation can be made in this area.It has been reported that use of creatine phosphate may have a favorable effect on mental deterioration in "cardio-cerebral syndrome" following heart attacks in the elderly.

Numerous studies suggest that creatine may be helpful in the treatment of various neuromuscular diseases, such as amyotrophic lateral sclerosis (ALS) and myasthenia gravis, and may delay onset of symptoms when used as an adjunct to conventional treatment. However, creatine ingestion does not appear to have a significant effect on muscle creatine stores or high-intensity exercise capacity in individuals with multiple sclerosis and supplementation does not seem to help people with tetraplegia.Although early studies were encouraging, recent research reports no beneficial effects on survival or disease progression. Additional studies are needed to provide clearer answers.