Author Affiliations 1School of Laboratory Medicine and Medical Sciences [SLMMS], College of Health Sciences, University of KwaZulu-Natal, Westville Campus South Africa 2School of Medical Science and Pathology, Faculty of Health Care Sciences, University of Limpopo, South Africa Received: April 24, 2020 | Published: April 30, 2020 Corresponding author: Kabelo Mokgalaboni, School of Laboratory Medicine and Medical Sciences [SLMMS], College of Health Sciences, University of KwaZulu-Natal, Durban 4001, Westville Campus South Africa DOI: 10.26717/BJSTR.2020.27.004489 Background: Metformin is used as a first-line treatment in patients with type 2 diabetes mellitus and have a significant impact on the prevention of complications associated with type 2 diabetes mellitus. Aim: To evaluate the effect of metformin treatment on vitamin B12 level and associated events in patientsliving with type 2 diabetes mellitus and further evaluate the efficacy of this drug in the prevention ofcardiovascular disease associated with type 2 diabetes mellitus. Methods: A literature search was conducted on PubMed-Medline database up to the 07 March 2020. Elevenstudies investigating the impact of metformin in type 2 diabetes mellitus were included in final synthesis after critical evaluation. Result: Metformin increases risk of vitamin B12 deficiency OR, 95%CI[2.41 [1.58,3.68], p Conclusion: In this meta-analysis, we conclude that metformin in patients with type 2 diabetes mellitus is associatedwith an increased risk of vitamin B12, stroke, retinopathy, anaemia, neuropathy and myocardialinfarction. Secondly, it prevents cardiovascular diseases and hypertension. Keywords: Metformin; Type 2 Diabetes Mellitus; Vitamin B12, Cardiovascular Disease, Neuropathy