I always get them impression that sanctions are used more to prove political points than bring about real change:
"Look how bad that regime is - the people don't even have food and medicine"
... because food and medicine are controlled.
Of course companies manage to still make money and bypass the senctions! I'd love to hear a cohesive argument for sanctions against Cuba for instance other than "they are communist" (which seems to have been the whole raison-de-etre for being unfriendly).