But don't just take Alex's word for it, True Value says:
Exterior paint is not durable for inside use. It may chalk excessively and/or the paint would not stick to the surface if it needs to be repainted. Exterior paint also contains mildewsides/fungicides that may smell when there is high humidity. It can even pose a health hazard due to the greater concentration of these mildewsides that are not normally used inside. Exterior paint used indoors may also worsen allergies.