Background Information
Creatine is an amino acid-like compound found in meat and fish. It is also synthesized in the liver from three amino acids (arginine, glycine, and methionine). This extremely popular ergogenic aid has undergone considerable study since its beneficial effects on strength/anaerobic performance were suggested in the early 1990s.

 Effects on Performance
Clearly, substantial, but not all data indicate that a loading dose of creatine (usually as creatine monohydrate) in doses of about 20 grams/day over 5 days does enhance intense, brief exercise performance, especially if it is repeated with short recovery intervals. Although variable among individuals, the gain in performance is usually about 10%. Gains may be less in body mass-dependent activities because even acute supplementation (3-5 days) typically results in increased body mass (about 1 kg in young men) due to increase muscle content of creatine, phosphocreatine, and water. Apparently, there are no benefits for endurance events. Most studies have used male subjects and women may experience smaller effects. Other than the body mass gain, side effects at least with acute creatine loading (3-5 days) appear to be limited to minor gastrointestinal disturbances (osmotic diarrhea) if the creatine monohydrate powder is not well mixed prior to ingestion.

The explanation for the improved performance with creatine loading involves enhanced energetics. Specifically, creatine appears to work by providing more available muscle phosphagens prior to exercise bouts and especially so when the exercise is very intense with short recovery intervals, by reducing changes in muscle pH because phosphocreatine use consumes hydrogen ions, and/or by stimulating other energetic pathways via accumulation of metabolites (creatine and inorganic phosphate). In addition, these ergogenic effects might allow on to train more intensely producing a further performance enhancement over time (i.e., a super training effect).

The typical loading dose is about 20 grams/day or about 285 mg/kg body mass (usually divided equally into 3 or 4 aliquots and ingested throughout the day). This represents about 10X the daily creatine turnover and would be essentially impossible to obtain without supplementation, as it would require a meat/fish intake of at least 4 kg/day. Importantly, a similar muscle creatine concentration can be attained with much smaller intakes of creatine (as little as 43 mg/kg per day) over 4 weeks. This dosage may be approached in the diet of individuals who eat significant amounts of meat and fish. Prolonged intake of loading doses (20 g/day) of creatine are unlikely to be beneficial because there appears to be an upper limit for skeletal muscle storage around 160 mmol/kg. Moreover, continued high extracellular creatine concentration caused the muscle creatine transporter to down-regulate leading to a large increase in urinary excretion and potential problems if the surplus creatine accumulates in other body tissues. Most importantly, these high intakes are unnecessary as maximal muscle creatine concentrations once attained can be maintained with much lower intakes (28-40 mg/kg per day). Co-ingesting creatine with carbohydrate and/or sodium is likely helpful as the creatine transporter is positively influenced by both. In addition, prior exercise appears to enhance muscle uptake. These effects may be important for individuals who seem to be resistant to creatine loading. Although the study of long term creatine use is in its infancy, based on sales figures and the absence of reported problems it would appear that weeks, months, and/or years of creatine use does not involve significant risk. Kidney damage due to prolonged creatine use, although frequently suggested, is likely overestimated. In contrast, there is evidence that creatine accumulates in other tissues including the brain and its effects there are totally unknown. There is even one report demonstrating a cytotoxic effect of creatine. Although the significance of this observation is unclear as it only occurred in combination with other specific substance not typically present, this observation demonstrates a potential danger that cannot be ruled out without further study. Finally, although unrelated to the safety of creatine per se, the extremely large commercial market that now exists has resulted in poor quality control. As a result, several contaminants have been found in creatine produced by some manufacturers - just one more potential concern that needs to be assessed.

 Recommendation
Although the long term use of creatine supplementation cannot, at the present time, be considered without risk, safety concerns must be considered minimal if the following procedures are utilized.