Inter- and Intra-individual Variations in Metformin Pharmacokinetics - The Importance of Genes and Drug Interactions

Part 1: The investigators intend to investigate the inter-individual variation in metformin Area Under Plasma Concentration Curve (AUC) following a single dose of oral metformin based on the plasma concentration of metformin after 3 and 10 hours and urine collection for 24 hours . Part 2: The investigators intend to contribute with DNA and metformin AUC determinations from subjects from part 1 to a major international study that aime to highlight the Genome Wide Association (GWA) between the entire genome and variations in metformin pharmacokinetics (AUC) in a large group of healthy subjects and patients. Part 3: The investigators aim to investigate the potential interaction between codeine and metformin in the intestine. The investigators secondary objective in part 3 is to investigate if the plasma concentration of morphine increases when codeine and metformin are given together due to competitive inhibition of the Organic cation transporter 1 (OCT1) transport protein (in the liver). Furthermore, the investigators will measure lactate after metformin ingestion as a proxy for metformin's effect on the intestinal mucosa, both after oral and intravenous metformin