Creatine is synthesized by liver, kidney, and pancreas and is present in the diet in meat and fish.  The normal intake is 1-2 g/day.  It forms phosphocreatine and acts as a phosphate donor to generate ATP from ADP in the energy cycle. Cells have enough creatine for 10 seconds of high-intensity exercise. 

Although creatine is popular in athletic circles, extensive research has found that it has at best a minor benefit for athletic events requiring short bursts of energy.  While there are some interesting preliminary studies, at the present time, there is no evidence that creatine is a worthwhile supplement for any psychiatric and medical disease or disease prevention.

No Benefit After Knee Surgery: Patients did not benefit from creatine supplementation in a DB PC study during the first 12 weeks of rehabilitation after ACL reconstruction. The Effect of Creatine Supplementation on Strength Recovery After Anterior Cruciate Ligament (ACL) Reconstruction: A Randomized, Placebo-Controlled, Double-Blind Trial. Tyler TF, Nicholas SJ, Hershman EB, Glace BW, Mullaney MJ, McHugh MP. Am J Sports Med. 2004 Mar-Apr;32(2):383-8

Creatine Might Help Brain Function: Creatine plays a pivotal role in brain energy homeostasis, being a temporal and spatial buffer for cytosolic and mitochondrial pools of the cellular energy currency, adenosine triphosphate and its regulator, adenosine diphosphate. Oral creatine supplementation (5 g/day for six weeks) in 45 young adult, vegetarian subjects in a DB PC, cross-over study found supplementation had a significant positive effect (p < 0.0001) on both working memory (backward digit span) and intelligence (Raven's Advanced Progressive Matrices), both tasks that require speed of processing. Oral creatine monohydrate supplementation improves brain performance: a double-blind, placebo-controlled, cross-over trial. Rae C, Digney AL, McEwan SR, Bates TC. University of Sydney. Proc R Soc Lond B Biol Sci. 2003 Oct 22;270(1529):2147-50. Ed: This small, short study’s finding is unlikely to stand up in further research. It’s too good to be true.

Older Men: Creatine and Protein Supplements No Benefit in Resistance Training: In a DB PC of 42 men ages 48-72, assigned to (1) resistance training placebo (n = 10), (2) resistance trained creatine supplemented (n = 10), (3) resistance trained protein supplemented (n = 11), and (4) resistance trained creatine and protein supplemented (n = 11), the supplementation protocols had no added benefits. Does Nutritional Supplementation Influence Adaptability of Muscle to Resistance Training in Men Aged 48 to 72 Years. Carter JM, et al. University of Oklahoma. J Geriatr Phys Ther. 2005;28(2):40-47.

Creatine No Help for Huntington’s: In a 1-year DB PC study of 41 Huntington’s disease patients, creatine 5 g/day did not improve functional, neuromuscular, and cognitive status. Creatine supplementation in Huntington's disease: a placebo-controlled pilot trial. Verbessem P, Lemiere J, Eijnde BO, Swinnen S, Vanhees L, Van Leemputte M, Hespel P, Dom R. Leuven, Belgium. Neurology. 2003 Oct 14;61(7):925-30 

Creatine Small Benefit for Some Short Exercises Only: In 96 DB PC studies found in a literature search, creatine caused small but significant short-term changes in lean body mass for repetitive-bout laboratory-based exercise tasks no longer than 30 seconds (e.g., isometric, isokinetic, and isotonic resistance exercise), and upper-body exercise. Creatine does not appear to be effective in improving running and swimming performance. Effect of creatine supplementation on body composition and performance: a meta-analysis. Branch JD. Old Dominion University, Norfolk, VA. Int J Sport Nutr Exerc Metab. 2003 Jun;13(2):198-226

Creatine No Help for Elderly Fitness: In a 1-year DB PC study of 46 men ages 55-75, creatine 5 g/day did not beneficially impact physical fitness in men between 55 and 75 yr of age. Effects of creatine supplementation and exercise training on fitness in men 55-75 yr old. Eijnde BO, Van Leemputte M, Goris M, Labarque V, Taes Y, Verbessem P, Vanhees L, Ramaekers M, Vanden Eynde B, Van Schuylenbergh R, Dom R, Richter EA, Hespel P. Leuven, Belgium. J Appl Physiol. 2003 Aug;95(2):818-28.

Creatine: Synthesized by liver, kidney, pancreas and in meat and fish. Normal intake 1-2g/d. Forms phosphocreatine as phosphate donor to generate ATP from ADP. Cells have enough for 10 sec high-intensity exercise. 28-day DB 8 weightlifters 20g/d increased strength, wt, fat-free mass. 31 studies of repetitive under 30 seconds of exercise of high intensity finds modest improvement but no benefit for aerobic of longer duration. Well tolerated.

Creatine Helps High Intensity Exercise: Supplementation improves performance for single bout of high intensity exercise, e.g. sprinting, cycling, swimming, but not for long distance running. 20 g/d. Am J Clin Nutr 8/00, 72S:607-17. Ginseng studies mostly older and since 1994 studies no benefit found although some earlier DB studies show benefit. 72:628S

Creatine, Ribose, and Glutamate No Help with Weight Lifting: In a 28-adult 8-week DB PC study with resistance training, no benefit from the supplement was found. U Florida. Effects of effervescent creatine, ribose, and glutamine supplementation on muscular strength, muscular endurance, and body composition. Falk DJ, Heelan KA, Thyfault JP, Koch AJ. J Strength Cond Res. 2003 Nov;17(4):810-6

Creatine May Help Concussion: Lab animals fed creatine showed less brain damage after head injuries. Ann Neurol 2000;48:723-9

Creatine May Help Older Men: Medicine and Science in Sports and Exercise 4/29 /02. The men on creatine gained 7 percent to 15 percent in the strength of large muscles of the hip, chest and shoulders, but the comparison group made no such gains. The creatine group also took 6 percent to 9 percent less time to get up from a chair or walk heel-to-toe. The percentage gains in strength were in line with what younger people get.

Creatine Helped Memory, Brain Performance: Small DB PC 6 weeks, then 6 week washout, then crossover. 45 young adult vegetarians  took 5 g per day. Vegetarians or vegans were chosen for the study since carnivores and omnivores obtain a variable level of creatine depending on the amount and type of meat they eat - although to reach the level of supplementation in this experiment would involve eating around 2 kg of meat a day. Working memory was tested using a backward digit span test. Intelligence was tested using Ravens Advanced Progressive Matrices. Digit span improved from a number length of about 7 to an average of 8.5 digits. The supplement can make you a considerably less 'fragrant' person.  Creatine supplementation had a significant positive effect (p < 0.0001) on both working memory (backward digit span) and intelligence (Raven's Advanced Progressive Matrices), both tasks that require speed of processing. Oral creatine monohydrate supplementation improves brain performance: a double-blind, placebo-controlled, cross-over trial. Rae C, Digney AL, McEwan SR, Bates TC. Proc R Soc Lond B Biol Sci. 2003 Oct 22;270(1529):2147-50

Few adverse effects of long-term creatine supplementation in a 310-day DB PC study of 175 patients on 10 g/day. 3 had to stop due to diarrhea or nausea. Groeneveld GJ, Beijer C, et al. University Medical Centre Utrecht, The Netherlands. Int J Sports Med. 2005 May;26(4):307-13.