You would have to examine if it is a controlled/scheduled substance. Other rules may apply too. For example, spray paint is not illegal, but selling it to a minor in your state may be, same thing goes with the anti-meth-ingredient ID laws some states have for ephedrines. I think there are no laws prohibiting you from giving aspirin to someone, but the prilosec may have a 'non-prescription' dose that the prescription exceeds.