Using Vitamins
Vitamins are said to give your stats a boost but it actually just adds 10 EPs to the stat. To prevent people from cheating, your pokemon is only allowed to take 10 of a type of Vitamin, giving it 100 EPs. Here are the Vitamins and what they do:
Protein : +10 EV to Attack
Iron : +10 EV to Defense
Carbos : +10 EV to Speed
Zinc : +10 EV to Sp. Defense
Calcium : +10 EV to Sp. Attack
HP Up : +10 EV to HP
However, if you trained your Pokemon prior to giving Vitamins, the number of Vitamins you can use is decreased. Vitamins can only raise the EVs to 100 and not over it.
it was in the FAQ