Metformin is a widely used drug with a relatively good efficacy in diabetes treatment, a good safety profile, and the potential for use in other indications. The variability in the individual responses to metformin therapy is partially determined by genetic factors. This narrative review aimed to summarize information on single nucleotide variant (SNVs) in genes for transporter proteins associated with metformin pharmacokinetics and pharmacodynamics and/or the occurrence of adverse effects. The