Creatine (which comes from the Greek word “kreas”, meaning “meat”) is a molecule that is produced in the body from the amino acids arginine, glycine, and methionine. It's primarily made in the liver and (to a lesser extent) in the kidneys and pancreas.^[1][2] Creatine stores high-energy phosphate groups in the form of phosphocreatine. These phosphate groups are donated to ADP to regenerate it to ATP, the primary energy carrier in the body.^[3] Creatine’s role in energy production is particularly relevant under conditions of high energy demand, such as intense physical or mental activity.

Creatine can be found in some animal-based foods and is most prevalent in meat and fish.^[4][5] Athletes commonly take it as a powder or in capsules.

The primary benefit of creatine is an improvement in strength and power output during resistance exercise. Creatine is well-researched for this purpose, and its effects are quite notable for a supplement, both in the general population,^[6][7][8][9] and specifically in older adults.^[10][11][12] When used in conjunction with resistance exercise, creatine may modestly increase lean mass.^{[7][12][11][13]} In trained athletes, creatine has been reported to reduce body fat and improve some measures of anaerobic exercise performance, strength, and power output.^[14][15] Creatine has also been tested for effects on anaerobic running capacity in many studies, the results of which are rather mixed but generally suggest a small improvement in performance.^{[16][17][18][19]}

Although creatine has been researched far less for cognitive performance and mental health than for physical performance, it may have benefits in some contexts. Creatine appears to reduce mental fatigue in some scenarios, particularly highly stressful ones involving sleep deprivation or exercise to exhaustion.^[20][21] Creatine may also improve some aspects of memory, particularly for people with below-average creatine levels, such as vegetarians and older adults.^[22][23] There is also some preliminary evidence to suggest that creatine may reduce symptoms of depression in individuals with major depressive disorder or bipolar disorder.^[24] That said, more research is needed in these areas and on other cognitive measures before creatine can be said to be effective for cognitive performance or mental health.

Supplementation with creatine typically results in weight gain, partly due to an increase in total body water.^[25] The range of weight gain after a creatine loading phase tends to fall between 0.9 and 1.8 kg (1.98–3.96 lbs).^[26][27] This may be of particular concern to individuals competing in weight-sensitive sports.

Diarrhea can occur when too much creatine is taken at one time,^[28] in which case the doses should be spread out throughout the day and taken with meals.

Supplementation with creatine has been reported to negatively affect aerobic capacity to a small degree.^[29] It has been speculated that this potential detrimental effect may be related to increases in total body water and body weight following supplementation with creatine.^[30]

Creatine works mainly through its effects on energy metabolism. Adenosine triphosphate (ATP) is a molecule that carries energy within cells and is the main fuel source for high-intensity exercise. When cells use ATP for energy, this molecule is converted into adenosine diphosphate (ADP) and adenosine monophosphate (AMP). Creatine exists in cells in the form of creatine phosphate (or phosphocreatine), which donates a high-energy phosphate group to ADP, thus turning this molecule back into ATP.

By increasing the overall pool of cellular phosphocreatine, supplementation with creatine can accelerate the recycling of ADP into ATP, thereby quickly replenishing cellular energy stores. This increased availability of energy can promote improvements in strength and power output.^[31] The pro-energetic properties of creatine don’t just affect skeletal muscle, but nearly all body systems, including the central nervous system (which comprises the brain and spinal cord).^[32]