According to the NY Times (Iran Sanctions Take Unexpected Toll on Medical Imports) the US sanctions against Iran are causing an unexpected shortage of medicine in Iran. After the heavy fines that the US has imposed on banks for past transactions with Iran banks have now become anxious to have anything to do with Iran and they refuse even transactions that are not forbidden by sanctions - like medicine sales.
But rather than considering this "unexpected" I think this is the logical consequence of Obama's view of trade as an arm. I am fundamentally opposed to that policy as it undermines the foundations of free trade.
Besides that it is well known that trade sanctions don't work and only strenthen sitting regimes. It it much better to have symbolic sanctions that clarify your position without imposing major harm.
According to Reuters (Sanctions side effect hits Iran's food system) Iran's food import has been similarly affected.