These grey berries (or are they pills?) are the equivalent of Phantasy Star IV's CUREPARAL item. When a party member is inflicted with paralysis in battle, they cannot move until treated with either a technique or this item. Paralysis is an affect that remains in play after a battle, so it is important to cure it. Otherwise, you might run into a more powerful enemy with one of your party members still out of commission.
You may view the gallery page for
CureParal.