Metformin is the most commonly used drug for type 2 diabetes in the world. Unfortunately, metformin has also been shown to inhibit the absorption of vitamin B1 from the intestines. So, in addition to the excessive loss of vitamin B1 through urination–as is the case in diabetics– the use of metformin puts diabetics at even greater risk of vitamin B1 deficiency, a well-established cause of peripheral neuropathy.
Metformin also inhibits the absorption of vitamin B12. As is the case with vitamin B1, vitamin B12 deficiency is also a well-established cause of peripheral neuropathy.
Many physicians recommend a high-potency bioactive form of vitamin of vitamin B1 as well as vitamin B12 for their patients on metformin.