Does metformin lose effectiveness over time? is it better to take it twice a day or is it once a day okay? i'm more consistent with once a day dosage.

Kind of...: Type ii diabetes is a progressive disease, as the Insulin producing beta cells eventually go through apoptosis/cell death. So most people will need to add additional medications as their body produces less and less insulin. So metformin is still doing it's job, but the body isn't. This beta cell death can be reduced with good diet and weight loss.