Each of the medicines that you use give you 10 ev points for the stats and the max you can use from medicines is 100 .
The max evs you can get per stat is 252 i.e. +63 stats for that particular stat .
The max evs you can possibly get is 508 or 510 so you can max only 2 of your stats .
You can ev train you pokemon by battling pokemon that give off a particular ev and you can use the wings that have come up in pokemon white/black that wield 1 ev point but can be used for more than 100 evs .