Most manufacturers recommend taking a multivitamin in the morning with a meal for the best results. This gives your body the whole day to process the nutrients when you can potentially use them. In athletes, for example, the B vitamins contained in a multivitamin taken with breakfast may help with energy production during training later in the day. Even so, you can take a multivitamin any time of day, but it's usually best to take them with food to avoid any potential nausea.