If you're taking folate tablets, your doctor will need to monitor your blood to check that they are working. You will be asked to have a blood test shortly after you start treatment and again after 8wks to confirm that your treatment has been successful. Most people need to take folic acid for only 4mths and they see an improvement in their symptoms within this time. However, some people need to take folic acid for longer periods of time and sometimes for life if the cause of the deficiency isn't resolved.
Attribution: BUPA