Lidcocaine is the numbing agent, make sure it is part of the formula. The numbing only lasts a short time as it is NOT systemic, but topical. So basically numbs on contact, unlike a painkiller like codeine or oxy that works systemically through the bloods stream. So ideally he should use it before he eats or drinks his nutrition, and he should take his pain meds maybe 15 minutes to an hour before (though the patch is usually a continuous does delivery so this isn't an issue) then swish with his mouthwash beforehand and eat or drink. best of luck.