Probably not, but for healthy people there’s little or no evidence that megadoses of those B vitamins are useful, either. Only B6 has been linked to a possible side effect, nerve damage. And that was at higher doses—7,000 percent of the daily value (DV), taken long-term—than you’re taking. Megadoses of B12 appear to be safe, since studies of pernicious-anemia treatment with injections of more than 40,000 percent of the DV haven’t reported any side effects. Thiamin and riboflavin also appear harmless because the body absorbs only a fraction of the huge doses; the rest is excreted in the urine.