Creatine is one of the most popular supplements among athletes seeking to build muscle mass and improve performance.
A substance that occurs naturally in the body and that is found in many foods, creatine is also marketed in a variety of advanced products often touted as legal steroids. These products come with varying price tags, varying claims of superiority, and with varying recommendations that they be ingested before exercise, after exercise, combined with other supplements, or through loading large quantities in a relatively short amount of time.
While there is significant evidence that creatine taken orally can provide substantial benefit to athletes, research doesn't support some of the more dramatic claims, regimens, or warnings.
Creatine is produced in the liver, kidneys and pancreas and stored in muscle tissue. It helps replace phosphates in the muscles that are lost during exertion through the depletion of ATP (adenosine triphosphate). This phosphate replacement helps produce energy, and creatine's role in this process is its most prominent attribute.
However, there is evidence that creatine can also promote muscle growth. A study published in 2000 found that subjects who took 20 grams of creatine a day for five days saw significantly increased fat-free mass and total body mass compared to a placebo, with no changes in body fat .
While the effect on muscle growth is still the object of considerable study, it is widely believed that the muscle growth occurs partly because the additional energy creatine produces will allow an athlete to do more work, and partly because creatine causes muscles to hold more water and become volumized through super-hydration. Additional muscle volume, in turn, not only reduces the breakdown of muscle protein, but it also promotes the synthesis of protein and an increase in the size and strength of muscle fibres .
Numerous studies have shown creatine can improve athletic performances of short-duration and high-intensity, such as sprinting . However, a Swedish study of creatine use in events requiring sustained exertion concluded that it actually diminished performance among trained endurance runners (researchers speculated that performances may have been diminished among distance runners because of the additional weight gained during their use of creatine) .
A Pennsylvania State University study of creatine use combined with a weight-training program over a 12-week period found significant gains in muscle size and strength compared to exercise alone. Creatine users experienced a 24% strength gain in the bench press, a 32% strength gain doing squats, and double the gain in muscle .
A Canadian study showed that selected muscles could be bulked up when athletes consume creatine supplements immediately after training. Thirteen men and 11 women who took part in a six-week resistance training program for arms and legs experienced increases in elbow flexor muscle thickness among those who used creatine supplements that were greater than found among those who took placebos. A similar effect was found in the knee extensors, but it did not reach statistical significance .
Creatine is found naturally in meats, fish, dairy products, egg whites, nuts and seeds, which may explain why vegetarians – who by definition don't eat meat or fish – usually respond well to supplementation . Vegetarian or not, it is very hard to consume enough food to provide as much creatine as supplementation
Creatine has been found effective when taken orally, with typical dosages ranging from 3-10 grams per day over an extended period (about 4-5 weeks). Bodyweight can also be used as a guide to dosage, with ingestion equalling about 0.06 grams per kilogram of weight (0.27g/lb).
An alternative protocol involves an initial loading phase of around 20g of creatine monohydrate each day (4 x 5gram servings during the day) for five days. This is followed by a maintenance phase in which the dosage is reduced to 3-5g per day. There is little evidence to show that a loading phase is necessary  and lower doses of creatine (3grams per day) over a 30-day period produces the same benefit as loading it over a six-day period . Keep in mind that muscles can store a finite amount of creatine and once this upper limit is reached any excess is flushed out of the body.
Research indicates that taking creatine with some carbohydrate can increase it's uptake . In the wake of the low-carbohydrate diet craze, research showed that combining creatine with a daily intake of 1,000 grams of lipoic acid also increases creatine uptake. Meanwhile, high doses of caffeine can block the effects of creatine by inhibiting muscle relaxation .
Despite commercial manufacturers' claims about the supposed advantages of "effervescent", "micronized" or "ethyl ester" creatine products over regular creatine monohydrate, there is little evidence to support such claims.
Creatine serum is a more recent addition to the market that makes bold claims. Sold as "ready-mixed" (as opposed to powdered creatine monohydrate), it's considerably easier to prepare and take. However, research has questioned both the contents [14,15,16] and effectiveness of this product [17,18]. Not only has Creatine Serum been found to contain very little creatine (and less than was stated on the bottle), it was shown to be ineffective at improving performance.
Some negative side-effects have been attributed to the use of creatine, such as pulled muscles, cramps, spasms, and increased difficulty in losing fat. However, research has shown that even minor side effects are rare  with longer-term studies finding no negative side effects over a period of several years [11,12,20].
As for more serious side effects such as kidney and liver damage, short to long-term studies (up to 5 years) have yet to find any adverse effects from creatine supplementation [12,20,21,22]. However, anyone with existing liver or kidney disease should consult their doctor before taking creatine.