Do people overdose on multivitamins?

Yes: One can overdose on anything, even water, but it's difficult to overdose on multivitamins unless they contain iron. It can be hazardous to take too much iron- a dose of over 1000 mg of elemental iron can be toxic. Pregnant women should avoid too much vit a, very high doses of b6 can cause neuropathy etc. So it depends on you, your individual needs & the type of multivitamin you are taking.