This is perhaps the most prominent creatine myth among athletes. It is a post hoc fallacy and something that gets repeated so much that those with no prior knowledge of creatine will usually and regrettably accept it to be fact.
If an athlete who happens to be using creatine gets a muscle cramp they will point the finger at their creatine use, when in reality the cramp is most likely due to lack of hydration, improper electrolyte balance, or variety of other factors that can result in cramping.
In a recent and very large (nearly 1500 participants) study, creatine supplementation did not result in increased incidence of cramping amongst athletes. In fact, the groups using creatine actually suffered from less cramps than the non-creatine group. (Dalbo, Roberts, and Kersick)
In a similar vein, many athletes mistakenly believe that creatine will heighten their risk of injury. However, research has demonstrated that creatine does not increase the likelihood of injury.
Quite to the contrary actually; a study conducted using 72 NCAA division 1 football players as subjects found that the athletes supplementing with creatine experienced less muscle cramps, muscle tightness, muscle strains, dehydration and total injuries. (Mayhew, Mayhew, and Ware)
Perhaps even more interesting is a 2001 study that showed creatine supplementation to speed up the progress of subjects placed on a rehabilitation program following immobilization (having a limb placed in a cast for an extended period). (Hespel, et al)