I have B12 def and it is believed to be caused by long term use of metformin. It seems my body cannot get the required B12 from diet, so I have injections. But I've seen on forums that B12 is not effective without folate or folic acid. I have no prescription for these. If I buy and swallow tablets, how do I know if my body can absorb these if it cannot get B12 from diet or tablets?