Unless you regularly eat liver, most people are vitamin B12 deficient and the usual form of B12 in supplements is cyanocobalamin. The problem with cyanocobalamin is that the cyanide ion is extremely tightly bound to cobalt thus making the vitamin all but useless. I recently switch to a mixture of adenosyl and hydroxycobalamin (these are the naturally occurring forms) that I got off amazon and I completely remedied my insomnia and chronic fatigue. The results were so profound I had to post it somewhere… just saying.