This article talks about negative (and some positive) effects of certain vitamins on people with heavy metal toxicity.
I thought it was pretty interesting (especially what it says about vitamins B12, D, and C). I personally have better results supplementing with cyanocobalamin than methylcobalamin (I seem to need to supplement vitamin B12 regularly, and I probably have chronic mercury toxicity). I have seemed to have noted negative effects with methylcobalamin, even though it's supposed to be more bioavailable. What's interesting, though, is vitamin D improves my symptoms (which, if the article spoke truly, it and other things in the article support my hypothesis about me having chronic mercury toxicity, and makes it less likely that I have other heavy metal concerns—but don't worry; I've been studying this for over a decade, and I'm not basing all my thoughts on this one article, nor am I making conclusions; I'm just dealing in possibilities).
Anyway, I should probably be sure not to let vitamin C and B12 drinks touch my fillings—and to stop chewing up my vitamin B12 tablets (if the article is true, that's just asking for problems). I don't see myself paying high prices for adenosylcobalamin, however. Maybe I'll just eat tomatoes with my vitamins instead.