Creatine Safety, Tolerability, & Efficacy in Huntington's Disease (CREST-E)

Inclusion Criteria: * Male or female ages 18 or older. * Clinical features of HD AND confirmatory family history of HD; OR Clinical features of HD AND CAG repeat expansion greater or equal to 36. * Stage I or II of illness (TFC greater or equal to 7). * Ambulatory and not requiring skilled nursing care at the time of enrollment. * Must be capable of providing informed consent and complying with trial procedures. * Additional inclusion criteria apply. Exclusion Criteria: * History of known sensitivity or intolerability to creatine monohydrate. * Exposure to any investigational drug within 30 days of randomization (Baseline visit). * Use of supplemental creatine at a dose greater than 10 grams within 30 days of randomization (Baseline visit). * Screening laboratory abnormalities that in the judgment of the investigator would jeopardize safe conduct of study. * Clinical evidence of unstable medical illness. * Clinical evidence of unstable psychiatric illness. * Additional exclusion criteria apply.