Can You Take Too Many Vitamins?

The risk of adverse effects is higher with what’s called megadosing, which involves taking much more than the recommended amount.

While megadose amounts aren’t officially established, "usually it’s a dose much higher than people consume in foods," says Fang Fang Zhang, MD, chair of the division of nutrition epidemiology and data science at Tufts University in Boston. These doses (often listed as 500 percent or 1,000 percent of the Daily Value) can sometimes be found in widely available supplements.

It’s often assumed that water-soluble vitamins, which you excrete, don’t pose the toxicity risk of fat-soluble vitamins, which your body absorbs. But even some water-soluble vitamins can be dangerous in excessive amounts, especially when taken for an extended period. "When taking B₆ in excess of 200 mg a day for an extended period of time, it can cause degeneration of the nerves and neuropathy," says Joel Mason, MD, at Tufts University.