Overlawyered rounded up a few links on how Pill Boxes are technically illegal in many places (and when crossing the boarder) when used to carry prescription medicines.
Even though they are technically illegal in many places, they are also technically allowed through TSA check points. TSA recommends, but does not require that the medication be labeled.
(I also found out that previous-liquids that are now solid are allowed through screening unless they are starting to melt. It makes me wonder how much moisture counts as “melted” and how fast you would need to run from freezer-to-check point to even invoke that rule)