Is multivitamin is more effetive if taken in split doses, half in the morning and half at night?

Probably, however...: This is likely true as many vitamins (most of the b's and vitamin c) can't be stored so little if any of what you take of these in the morning is around at night. Some vits are designed to take with each meal. However, some people find that taking vitamins at night is stimulating and can cause difficulty sleeping. If this is the case you could try splitting doses in morning and afternoon.

Not Really: Multivitamins are generally worthless for most Americans on any normal diet at any time. Unless you are on a very restricted diet, pregnant, or fighting a chronic disease, you do not need it. If you have a specific lab proven vitamin deficiency, then take that one. Otherwise, save your money and get a gym membership. Exercise has proven health benefits, while multivitamins do not.