I have been on the maxium amount of Phenergan for about six months for nausea and I think I have almost become immune to it's effects. It doesn't help as much anymore, and doesn't make me even the tinest bit drowsy anymore either. When your body gets used to a medication, if you stop it for a while would that make it start working again? Or is it like once your immune to it, your immune to it forever? Also, can this happen with all medications? I sure hope not...