Peak plasma concentrations (Cmax) are reached within 1–3 hours of taking immediate-release metformin and 4–8 hours with extended-release formulations. The plasma protein binding of metformin is negligible, as reflected by its very high apparent volume of distribution (300–1000 L after a single dose). Steady state is usually reached in 1–2 days.Metformin has acid dissociation constant values (pKa) of 2.8 and 11.5, so it exists very largely as the hydrophilic cationic species at physiological pH values. The metformin pKa values make it a stronger base than most other basic medications with less than 0.01% nonionized in blood. Furthermore, the lipid solubility of the nonionized species is slight as shown by its low logP value (log(10) of the distribution coefficient of the nonionized form between octanol and water) of −1.43. These chemical parameters indicate low lipophilicity and, consequently, rapid passive diffusion of metformin through cell membranes is unlikely. As a result of its low lipid solubility it requires the transporter SLC22A1 in order for it to enter cells. The logP of metformin is less than that of phenformin (−0.84) because two methyl substituents on metformin impart lesser lipophilicity than the larger phenylethyl side chain in phenformin. More lipophilic derivatives of metformin are presently under investigation with the aim of producing prodrugs with superior oral absorption than metformin.Metformin is not metabolized. It is cleared from the body by tubular secretion and excreted unchanged in the urine; it is undetectable in blood plasma within 24 hours of a single oral dose. The average elimination half-life in plasma is 6.2 hours.
The FDA is also collaborating with international regulators to share testing results for metformin.In July 2020, Lupin Pharmaceuticals pulled all lots (batches) of metformin after discovering unacceptably high levels of NDMA in tested samples.In August 2020, Bayshore Pharmaceuticals recalled two lots of tablets. Research
Metformin has been studied for its effects on multiple other conditions, including:

Non-alcoholic fatty liver disease
Premature puberty
Cancer
Cardiovascular disease in people with diabetes
AgingWhile metformin may reduce body weight in persons with fragile X syndrome,  whether it improves neurological or psychiatric symptoms is uncertain. Metformin has been studied in vivo (C. elegans and crickets) for effects on aging. A 2017 review found that people with diabetes who were taking metformin had lower all-cause mortality. They also had reduced cancer and cardiovascular disease compared with those on other therapies. References
Further reading
External links

"Metformin". Drug Information Portal. U.S. National Library of Medicine. "Metformin hydrochloride". Drug Information Portal. U.S. National Library of Medicine.