Tonks is right. As far as truth potions go in our world, Veritaserum is the strongest, and people just don't walk around blabbing the truth. It's definitely 'glazed over' as she said. Some potions are stronger than others too.
But basically it does just what it says, it makes you tell the truth, and compels you to tell the truth. Considering all the different kinds of magic here, a truth potion is possible. They'd just have to find a way to get it to everyone.