Methyl succinate partially reverses metformin's effects. When 12.5 mM methyl succinate is added to complete growth media, the 48 hour growth inhibition effects of metformin on PA-1 are reduced. Methyl succinate serves as an alternate energy source to glucose that bypasses complex I in the electron transport chain. Metformin at higher doses can overcome the reversal of growth inhibition provided by methyl succinate. * p < 0.01.