vitamin b12 deficiency
"I have been eating a plant based, whole food diet (vegan) for the last year and taking this form of b12 every day.  I take 1000 mcg twice daily and this has not helped at all.  I have become more and more tired and just don't have energy to do the normal activities of daily living.  I have been researching and found many people can not utilize this form of cobalamine and have taken methylcobalmine with great success.  I took my first dose tonight and will report back.  There was even a doctor who reported that in his practice he found the above information to be true with respect to oral supplementation.  He did say that injections of cyanocobalamine worked but the oral form failed.  Sublingual methylcobalamine did work with his patients."