Folic acid
Folic acid is the stable synthetic form of folate, a B vitamin available over the counter. It is converted in the body to the coenzymes that carry single-carbon units for DNA synthesis and for the remethylation of homocysteine, which is why deficiency impairs the production of rapidly dividing cells such as red blood cells. It is taken to correct or prevent folate deficiency.
Timing is not critical and it can be taken with or without food. The one thing worth knowing is that folate corrects the anaemia of vitamin B12 deficiency while doing nothing for the nerve damage, so it can mask a B12 problem until it is advanced; for that reason B12 is usually checked alongside folate before and during supplementation. Folate, homocysteine and B12 are the values that show whether the deficiency is being corrected and whether something else is being hidden.
See a doctor before continuing if B12 status is unknown or low, and see a doctor if tingling, numbness, weakness or balance problems develop while taking it.
Reference information, not medical advice. Discuss any change with your doctor.