B12 deficiency mainly due to impaired absorption from the intestine, due to some causes, apart from intrinsic factors deficiency and some drugs, those potentially impair B 12 absorption. Unless the drugs ( PPI, H2 blocker, metformin, antacid, cholcicine, alcohol, some anticonvulsant, MTX , sulphasalazine and others) those cause impaired absorption of the vitamin 12 , are not stopped, no oral preparation would be effective. So in these cases parenteral route should be the route of choice. In several elderly patients suffering from knee joints pain we have treated with B12 successfully. In a patient (55yrs) of Parkinson's disease suffering for the last 20 yrs, 1 mg daily intramuscularly for 20 days abated 50% of the symptoms in one and half month.