Folic acid should never be given alone or in conjunction with inadequate amounts of vitamin B12 for the treatment of undiagnosed megaloblastic anemia, since folic acid may produce a hematopoietic response in patients with a megaloblastic anemia due to vitamin B12 deficiency without preventing aggravation of neurological symptoms. This masking of the true deficiency state can lead to serious neurological damage, such as subacute combined degeneration of the spinal cord.