Hope this helps, I found it on: http://www.mend.net/cgh/methylcobalamin.html

Methylcobalamin is the only active form of Vitamin B-12 in the brain outside the mitochondrion. The liver must convert cyanocobalamin to methylcobalamin in order for Vitamin B-12 to do its biochemical work in the brain. When the complex conversion of cyanocobalamin is not completed, the brain is robbed of the benefits of methylcobalamin. Cyanocobalamin is a by-product of Vitamin B-12 charcoal extraction. Scientific methods led people to believe that cyanocobalamin, not methylcobalamin was the naturally occurring form of Vitamin B-12. Cyanide in the charcoal replaces the methyl group in much the same way as it does in the body of a cigarette smoker. Vitamin B-12 requires the assistance of Intrinsic Factor to enter the body from the small intestine. Without Intrinsic Factor, dietary Vitamin B-12 or B-12-containing supplements go unabsorbed.

Thanks for all the wonderful information. I am looking into for my son . not sure if at 19 it will work

Additionally, I have recently read that certain other supplements can boost the effectiveness of the mB12. DMG, folinic acid (active form of folic acid) and one of the active forms of B1 like TTFD or Benfotiamine in particular have been mentioned as having a synergistic effect with mB12.

my son gets methyl b12 transdermally and we have noticed a slight difference in him... not really enough to say either way if it is effective...

Yes, there is preliminary research suggesting that it is helpful in a subset of kids with ASD and more research is ongoing. My DD is one of the very last participants in a study at UC San Francisco on it. The professor who is running it told me that based on the preliminary results, they're seeing about 1/3 of the kids get major improvement, 1/3 get no improvement, and the remaining 1/3 get mixed results (improvement but also side effects). I told that to our biomed dr. and he said that's about the same split he sees in his patients who try mB12.