Vitamin B12 (cyanocobalamine) deficiency is known to cause a wide variety of neurological symptoms.   It also seems to produce facial neuralgia, according to a report presented at the International Headache Congress in Philadelphia a week ago.  Two physicians from Milwaukee described 17 patients who had facial pain that was not typical of trigeminal neuralgia because they had no trigger area and had numbness on the affected side.  They all had vitamin B12 deficiency and they pain improved with injections of vitamin B12.  In a previous post I mentioned another study that found an association between migraine headaches and high homocysteine levels, which can also be caused by vitamin B12 deficiency.  Oral absorption of vitamin B12 supplements is often inadequate and a nasal spray (which is expensive) or an injection are the best ways to correct this deficiency.