Creatine is an amino acid produced by all vertebrates, and in some invertebrates. The main function of creatine is to facilitate the energy process for muscles by acting as a buffering system for adenosine triphosphate (ATP), the primary cellular energy transport molecule. Creatine was first found in muscle tissue in 1832, though its role was not discovered until much later. Our bodies produce enough creatine for daily functions, and all vertebrate meat contains creatine as well, therefore ordinarily people have enough creatine. To clear one thing, creatine does not play any role in metabolizing fat, ingesting creatine will not increase breakdown of fat. However, as early as 1912, scientists found ingesting extra creatine can boost creatine supply in our muscles, and this has shown some improvements in performance, most noticeably in short-duration, high intensity activities such as sprinting, rowing, and weightlifting. Indeed, creatine has been proposed on several occasions and in several countries to be banned for use in competitive sports. As it turns out, these types of exercises are very effective in burning fat. Little research has shown any increased effects on long duration exercises however. Other claims, such as creatine increasing muscular mass, have not been backed by solid research. While weight gains have been shown by taking creatine supplementation, it has not been clear if the weight gain has been in the muscles.
Using creatine is a little different from using most supplements, in that the best improvements come from engaging in a "loading phase" first. What this entails is for the first week, sometimes two weeks, one takes about 15 to 25 grams a day, depending on bodyweight, spread throughout the day. After this phase, creatine is taken at doses ranging from 2 to 5 grams a day, depending on weight and activity level. Many claim pre workout usage of creatine has no effect or even a negative effect. Most athletes and fitness enthusiasts prefer a post workout dosage. Experimenting on myself, I found splitting between pre and post workout yields the best performance improvements, as well as an optimal dosage of 5 grams a day for cardio only days, and 7 grams for weights + cardio days. On days you don't workout, the common practice is to take creatine first thing in the morning. There are some concerns that long-term creatine supplementation can suppress the body's own ability to produce creatine. While there is no solid evidence to support this, many athletes practice "creatine cycling". All this entails is stopping creating supplements for a short period and then resuming again, sometimes with a loading phase. The most common practice is two months on creatine, one month off. You should be drinking lots of water anyway, but if you do decide to use creatine, it is important to stay well hydrated.
Since creatine is core to biological functioning, it has very few reported harmful side effects. There are some reports of excessive creatine supplementing can cause kidney problems, though the evidence in this is lacking. Still, if you have renal problems, consult with a physician before taking creatine. Some reports suggest creatine may increase water retention in muscles (which could be the source of confusion over creatine increasing muscle mass). Some people have not responded to creatine with any increase in athletic performance, however.
The bottom line is, creatine will not directly help with fat burning. If you are not engaging in high intensity activities, such as high intensity interval training (HIIT) or weightlifting, as part of your weight loss program, taking creatine will have no impact on losing fat, you are simply wasting your money. If, however, you do, say, HIIT cardio on a regular basis, taking creatine may allow you to do longer and more intense sessions. That in turn will allow greater fat burning each session, and therefore more weight loss in the same period of time. Using creatine for weight training could allow for heavier weights and that in itself could promote faster muscle growth. More muscle mass means more calories burned daily. For my pre-workout creatine, I prefer Optimum Nutrition's Creatine Powder; it is inexpensive and ON's products are very reliable in quality and purity. Post workout creatine, I use Muscle-Tech's Cell-Tech, which not only has creatine, it has dextrose, a fast acting carb, and other ingredients that seem to significantly help me with post-workout recovery. Because I split between the two, I use smaller dosages of each and that makes the costs manageable.