Side Effects of Metformin in Type 2 Diabetes Mellitus: A Systematic Literature Review

Background: Metformin is a Biguanide antihyperglycemic medication, is still considered as the best medications, and the first line of treatment either as monotherapy or in combination with other drugs for type 2 diabetes mellitus. Even though metformin has efficacy, very low risk of hypoglycemia and weight gain, and low cost, it also has side effects that can’t be ruled out. The aims of this study to evaluate of side effects of metformin in type 2 diabetes mellitus. Methods: Medline via (via Pub Med) from 2019 until 2024 in English. Term defining side effects of metformin were combined with the term type 2 diabetes mellitus during the search. The studies were chosen based on inclusion criteria. Results: There were 40 patients (53.3%) had gastrointestinal (GI) effects with persistent use of metformin tablet for 7.8 years in average, including epigastric and abdominal pain, nausea, vomiting, diarrhea, and bloating, and the other research showed that Metformin therapy can reduce testosterone levels in males with T2DM who had normalized blood control, that is indicated that the use of metformin may be another reason of the high prevalence of low testosterone levels in males with T2DM, the same thing also happens with vitamin B12 deficiency that there was a graded increase in the likelihood of vitamin B12 deficiency with increasing dose with those treated with > 2000 mg daily at nearly 40 times the odds compared with those not taking metformin. Conclusion: from systematic literature review study, it was found that there are side effects of metformin that cannot be ruled out, such as gastrointestinal (vomiting, diarrhea, bloating), decreased testosterone levels and deficiency vitamin B12.