Inclusion Criteria:  Symptomatic positive clinical diagnosis of Huntington disease. Presence of 36 CAG repeats (or more) in the hunting gene based on centralized CAG analysis. Men or women between 21-65 years of age, inclusive, with an onset of HD at 18 years of age or older. Women of childbearing potential (women who are not postmenopausal children or who have not undergone surgical sterilization at times) will need to be using a contraceptive method for 30 days before beginning study treatment, and will have contact with at least two methods of birth control throughout the duration of the study and up to 30 days after taking the last dose of treatment. A sum of > 4 points on the UHDRS-TMS scale and a diagnostic confidence level of 4. Scale of independence ≥ 75%. Score on the UHDRS-TFC scale ≥ 8 at the screening visit. They must be trained and willing to provide written informed consent prior to any procedure related to the study to be performed at the screening visit. Patients with a legal guardian must be determined according to local requirements. They must be trained and will require taking oral medication and will need to be determined to comply with the specific study procedures. They must be able to travel to the study center and, in the judgment of the investigator, demonstrate that it is probable that they can continue traveling during the study. Availability and willingness of a caregiver, informant, or family member to provide information during study visits that evaluate PBA-s. It is recommended that the caregiver be someone who cares for the patient at least 2 to 3 times a week and at least 3 hours per occasion. The suitability of the caregiver must be judged by the investigator.  Exclusion Criteria:  The participant has taken metformin in the last three months before the start of the study. The participant has diabetes of any kind. The participant is pregnant or lactating. The participant has a medical condition other than HD (metabolism, kidney function, liver function, heart problems, etc.), or any contraindication against metformin. The participant has an uncontrolled psychiatric condition. Participant is allergic to metformin or any of the other ingredients of this medicine. The participant has kidney problems [creatinine clearance <60 ml / min calculated using Cockcroft-Gault formula] or liver problems. The participant is dehydrated, from prolonged or severe diarrhea, or has vomited several times. The participant has a serious infection. The participant has been treated for heart failure or has recently had a heart attack, has severe circulation problems, or is having difficulty breathing. The participant drinks> 6 units / day of alcohol (alcoholism). Participants diagnosed with oncological disease. Participants with a suicidal propensity, with an affirmative answer in items 4 or 5 in the C-SSRS at the screening visit.