Can you overdose on vitamin supplements?

Yes: Certain vitamins, particularly the fat soluble ones, a, d, e, and k can reach toxic levels if you take too much. The other vitamins can cause other health problems, such as increasing risk for cancer, if taken in very high doses.

Yes: Fat soluble vitamins such as A, D, E and K will accumulate in body and cause harmful effects. High doses of other vitamins can also cause problems, e.g, Niacin causing vasomotor symptoms, excess pyridoxine may cause nerve damage, taking folic acid while deficient in B12 will cause nerve damage,