Creatine: Benefits, Dosage, and Safety

What creatine is

Creatine is a nitrogen-containing compound produced in the body and obtained in small amounts from animal-based foods. It is not a classical essential vitamin or mineral, so no Dietary Reference Intake has been set. The liver and kidneys synthesize about 1 g/day of creatine from the amino acids glycine, arginine, and methionine. In muscle it is stored partly as phosphocreatine, which regenerates ATP during brief, intense activity. A person weighing 154 pounds holds about 120 g of creatine plus phosphocreatine, almost all in skeletal and cardiac muscle. It is one of the most thoroughly studied and widely used sports supplements.

What it does

• Helps regenerate ATP, the immediate energy source for short-term, predominantly anaerobic muscle activity, by supplying phosphate through phosphocreatine
• Increases muscle stores of phosphocreatine used to generate ATP at the start of intense exercise
• Speeds re-synthesis of phosphocreatine after exercise
• May depress degradation of adenine nucleotides and accumulation of lactate
• May enhance glycogen storage in skeletal muscle
• Is metabolized to creatinine, a waste product cleared by the kidneys

Intake and dosing

Creatine is not an essential nutrient, so no Recommended Dietary Allowance or Tolerable Upper Intake Level has been set. Doses in studies vary widely. Because supplement doses are not standardised, discuss an appropriate amount with a clinician or pharmacist.

Deficiency and who is at risk

Creatine is not an essential dietary nutrient, so classic dietary deficiency is not defined; the liver and kidneys synthesize about 1 g/day. People with lower baseline muscle creatine, such as vegetarians and vegans, tend to have smaller muscle stores and may show a greater response to supplementation. Rare inherited creatine metabolism disorders are separate medical conditions, not dietary deficiency.

Who may need more

• Athletes doing repeated short bursts of high-intensity, intermittent activity such as sprinting and weight lifting
• People in resistance and strength-training programs seeking gains in strength, power, and training adaptation
• Vegetarians and vegans, who have lower baseline muscle creatine and may respond more to supplementation

Food sources

Animal-based foods: beef about 2 g/lb, pork about 2.3 g/lb, and salmon about 2 g/lb. Dietary intake supplies only small amounts; ergogenic effects require larger supplemental doses over time.

Forms and absorption

Creatine monohydrate is 88% creatine by weight and is the most widely used and studied form. Other, usually more expensive, forms (creatine ethyl ester, creatine alpha-ketoglutarate, and buffered forms) have not been proven superior to monohydrate for raising muscle creatine levels, digestibility, product stability, or safety. A typical protocol is a loading phase of 20 g/day in four 5 g portions for 5 to 7 days (or 0.3 g/kg body weight), then maintenance of 3 to 5 g/day. An alternative without loading is 3 to 6 g/day (0.03 to 0.1 g/kg body weight) for 3 to 4 weeks.

Safety, excess and interactions

Too much

Creatine most consistently causes weight gain from water retention (studies report a 1 to 2 kg increase in total body weight in a month during strength training). Anecdotal reactions include nausea, diarrhea and related gastrointestinal distress, muscle cramps, muscle stiffness, reduced range of motion, and heat intolerance. No consistent set of serious side effects has been identified at typical doses. No Tolerable Upper Intake Level has been established.

Interactions to know

• The ODS Exercise and Athletic Performance fact sheet does not list specific well-established drug interactions for creatine
• Creatine is metabolized to creatinine and excreted by the kidneys, so it is prudent to be cautious when combining it with nephrotoxic medications or in people with impaired kidney function (general clinical caution, not a specific ODS-listed interaction)

How status is measured

Creatine status is not routinely measured in clinical practice. Muscle creatine and phosphocreatine content can be assessed in research settings (for example by muscle biopsy or magnetic resonance spectroscopy). Serum creatinine, the waste product of creatine metabolism, may rise modestly with supplementation and is a kidney-function marker rather than a nutritional status test.

Regulated by the FDA as a dietary supplement under the Dietary Supplement Health and Education Act of 1994 (DSHEA), not approved as a drug to diagnose, treat, cure, or prevent disease. Manufacturers are responsible for safety and labeling; products are not pre-approved by the FDA for efficacy.

What the evidence supports

We grade the strength of evidence behind each common reason people take creatine, mirroring how the NIH describes it.