Here's some Hydroxycybl info I just came across in Amy Yasko's ebook, Autism, Pathways to Recovery. This might underlie why it works for some and not for others, although I'm of the category that she suggests hydroxy might work better for, and it didn't seem so to me. pg 145-6 This book is available as free pdf: http://www.holisticheal.com/autism-pathways-to-recovery-book-and-workbook.html "However, before supplementing with B12, please first take into account your COMT V158M and VDR/Taq status, which will help to determine whether to focus more heavily on hydroxyl B12 or methyl B12 for support. In my clini- cal experience, I’ve regularly observed that those with COMT V158M + and VDR Taq – mutations don’t tolerate methyl donors well, including methyl B12. Also adults, regardless of their COMT V158M/VDR Taq status, have more limited tolerance than children for the detox triggered by methyl B12. Despite that, those who are MTR + and MTRR + can and should look at higher-dose B12 support, balancing the ratio of methyl to hydroxyl B12 based on COMT V158M/VDR Taq status. As you gradually proceed to add in B12, you can also take into account your own or your child’s personal tolerance for it. In addition to either methyl or hydroxyl B12, I often suggest the use of low doses of cyano (to support the eyes) and adenosyl B12 with vitamin E succinate, as you will see in the supplement recommendations. "One way to begin B12 support is with one chewable methyl B12 (5mg) or hy- droxyl (1 or 2mg) daily, gradually increasing to two, three, or more per day if you can tolerate it. If mood swings occur, then decrease the dose of B12 back down to a more comfortable level. While a new nasal B12 is available, I don’t recommend using that exclusively. I prefer some B12 to be absorbed through the gut with the help of Intrinsic Factor, which is contained in some of the recommended supple- ments. In addition, the use of oral B12 sprays (available as hydroxyl or methyl,) topical B12 cream, B12 gum and the B12 patch are other means by which to support B12 in the body. I like to see multiple routes and forms of B12 used until I feel that the system has been saturated with B12 (see discussion of cobalt levels below). Literature suggests that oral B12 is as effective as injected B12. However, if preferred, you can consider B12 injections, making sure to use either plain methyl B12 (without any added folinic or NAC) or plain hydroxyl B12 injections. You can use the chewable B12 and the oral B12 spray on the injection “off days.” "If you plan to use injections, start with once per week, and gradually increase to three times per week. Allow your tolerance levels to determine how you can gradually increase the B12. As always work in conjunction with your health care provider."