Are there any negative effects of taking high doses of B12 and multi-b on a daily basis?

Vtiamin OD. I would get blood work done in an annual pyhsical and ask your dr to do a serum B12 level. If it is adequte you do not need b12 there is a lot of conflicting information on multivitamins. I am not sure what you mean by :"high doses" but I am sure if you follow the directions on the label of any multi you will be fine.