Is creatine safe?

Creatine is absolutely safe.

Creatine is one of the most thoroughly researched compounds, and no adverse side effects have been noted through supplementation.[1][2][3][4][5][6]

References

1.^Groeneveld GJ, Beijer C, Veldink JH, Kalmijn S, Wokke JH, van den Berg LHFew adverse effects of long-term creatine supplementation in a placebo-controlled trialInt J Sports Med.(2005 May)
2.^Greenwood M, Kreider RB, Melton C, Rasmussen C, Lancaster S, Cantler E, Milnor P, Almada ACreatine supplementation during college football training does not increase the incidence of cramping or injuryMol Cell Biochem.(2003 Feb)
3.^Lopez RM, Casa DJ, McDermott BP, Ganio MS, Armstrong LE, Maresh CMDoes creatine supplementation hinder exercise heat tolerance or hydration status? A systematic review with meta-analysesJ Athl Train.(2009 Mar-Apr)
4.^Greenwood M, Kreider RB, Greenwood L, Byars ACramping and Injury Incidence in Collegiate Football Players Are Reduced by Creatine SupplementationJ Athl Train.(2003 Sep)
5.^Shao A, Hathcock JNRisk assessment for creatine monohydrateRegul Toxicol Pharmacol.(2006 Aug)
6.^Bender A, Samtleben W, Elstner M, Klopstock TLong-term creatine supplementation is safe in aged patients with Parkinson diseaseNutr Res.(2008 Mar)