Ever since it was discovered that creatine could cause weight gain, a debate has raged over whether this increase in weight was from water retention or actual muscle gain.
A study by Jeff Volek, Ph.D., out of Penn State University is the first to measure the changes in muscle fiber size following creatine supplementation. After 12 weeks of supplementing with either a placebo or creatine (25 grams/day for one week followed by 5 grams/day for 11 weeks) and participating in a periodized weight training program, the creatine group increased lean body mass, maximum bench press, and maximum squat significantly greater than placebo. The creatine group also showed a greater increase in muscle fiber cross sectional area (i.e. the muscle fibers got bigger) than placebo. No negative side effects were reported with this enhanced physiology and performance. So it looks like creatine really does add muscle and not just water.