Uma edição do seu script:

local HP_PERCENT = 25 --%
local M_PERCENT = 25
function onUse(cid, item, fromPosition, itemEx, toPosition)
	ITEM = 2673
	local storage = 50000
	local wait = 0.7
	if fromPosition.x ~= CONTAINER_POSITION and exhaustion.get(cid, storage) == FALSE then
		REG_HEALTH = math.floor(getCreatureMaxHealth(cid) * (HP_PERCENT/100))
		REG_MANA = math.floor(getPlayerMaxMana(cid) * (M_PERCENT/100))
		doPlayerAddMana(cid, REG_MANA)
		doCreatureAddHealth(cid, REG_HEALTH)
		doCreatureSay(cid, 'Power is back !', TALKTYPE_ORANGE_1)
		doRemoveItem(item.uid, 1)
		exhaustion.set(cid, storage, wait)
	elseif item.itemid == ITEM and exhaustion.get(cid, storage) == FALSE then
		REG_HEALTH = math.floor(getCreatureMaxHealth(cid) * (HP_PERCENT/100))
		REG_MANA = math.floor(getPlayerMaxMana(cid) * (M_PERCENT/100))
		doPlayerAddMana(cid, REG_MANA)
		doCreatureAddHealth(cid, REG_HEALTH)
		doCreatureSay(cid, 'Power is back !', TALKTYPE_ORANGE_1)
		doRemoveItem(item.uid,1)
		exhaustion.set(cid, storage, wait)
	else
		doPlayerSendCancel(cid, "You are exhausted.")
	end
	return TRUE
end

Edite as variáveis HP_PERCENT e M_PERCENT.

O math.floor é pra não ficar valores "quebrados".