Inclusion Criteria:
* Sign the informed consent form prior to any study-specific procedure.
* Male or female, aged 40 to 75 years, inclusive, at the time of Screening.
* Have a COPD clinic diagnostic according to Global Initiative for Obstructive Lung Disease (GOLD) 2022 with a post-bronchodilator FEV1/FVC \<0.7 at Screening (Visit 1)
* Have a post-bronchodilator FEV1 \>40% ≤ 70% of the predicted value at Screening (Visit 1)
* Smoking history of more than 10 pack/years (\[number of cigarettes smoked per day x number of years smoked\]/20)
* Must have been able to understand and comply with the requirements of the study, as judged by the investigator.
* Have some kind of emphysema (centrolobulillar or paraseptal) reported by an expert radiologist.
* Have a certified decrease of the Lung Function in the last 3 years \>40 ml/ml per year of FEV1.
* Women in childbearing age with negative pregnancy test.
Exclusion Criteria:
* Participating in another clinic trial with any commercially or investigational biological medicinal product within 4 months prior to Screening.
* Patients who take oral corticosteroids chronically.
* Respiratory track infection history (superior respiratory tract included) and pulmonary exarcerbation within 6 weeks prior to Screening.
* Lung resection or lung volume reduction surgery within 12 months prior to Screening (Visit 1), or lung trasplant history, or, as judged by the investigator, patient may have required a thoracotomy or other lung surgery during the study.
* Known active tuberculosis.
* History of intersticial lung or massive pulmonary thromboembolic disease.
* History of bronchiectasis secondary to respiratory diseasesother than COPD (e.g. cystic fibrosis, Kartagener's syndrome, etc.).
* Any clinically significant disease or disorder (e.g. cardiovascular, gastrointestinal, hepatic, renal (GFR \< 30 ml/min), neurological, musculoskeletal, endocrine, metabolic, psychiatric, and major physical impairment) that, in the opinion of the investigator, could have placed the patient at risk for participation in the study, could have influenced the study results, or could have affected the patient's ability to participate in the study.
* Recent history (within 12 months prior to screening \[Visit 1\]) of myocardial infarction, recent history of heart failure (New York Heart Association \[NYHA\] classes III and IV), pulmonary oedema and/or cardiac arrhythmia.
* History of cancer (within 5 years prior to Visit 1), except non-metastatic skin cancer and non-melanoma.
* Patients who cannot perform spirometry manoeuvres or tolerate plethysmography.
* Contraindications to the use of metformin: allergy to the drug, advanced renal failure (CKD stage 3 and above), patients on dialysis, chronic metabolic or respiratory acidosis or liver cirrhosis.
* Patients with type 2 Diabetes Mellitus with or without previous use of metformin.
* Pregnant women, nursing mothers or women of childbearing age who are not going to use contraceptive methods.
