From the research I've done no matter the size of the dose your body can only absorb 1 to 2% of each dose. Which isn't alot. Also, I've been seeing that it's difficult to overdose on the B's. The only one you really have to worry about is the B-6. But I can't remember what was supposed to be too much. I also read that it's very important to get enough Folic Acid along with the B's. B-12 is water soluble just like Vit C. Too much Vit C sends you running to the bathroom alot and that's pretty much it. It's the fat soluble vitamins such as Vit A and others that are stored that can cause overdose problems.