That's not true. We have the drug ads in the US because legal precedent since the late-70s/early-80s (roughly) in the US now protects commercial speech.

Companies are legally considered persons, hence their speech is protected. This is consistent with individual sovereignty. If people are wards of the State, then the State would have the responsibility to police "harmful" speech; advocating untrained people to ask their doctor for a specific medication could be considered harmful speech (since apparently only two countries in the world allow it, and not even the US before the 70s-ish, apparently).