i bet you've never tried coke before wow?

Presumably certain drugs are forbidden due to the effect on other people, not only the effect on the person who is taking the drugs. So if a country has deemed that a certain drug has a negative effect on society, it would be hard to justify letting some people use it.

I see your point, it makes sense... but I think it goes against the reason why drugs (at least some drugs) are banned in the first place.

Dunno, this is a tricky subject. First off, many countries just wouldn't go for it... hell, many of those same countries actively persecute people based on religion anyway so that's not a shocker.

I could see something like this popping up in the west, though... the key component being that you had to be a citizen of the country from which you brought the medication. That would restrict drug trafficking and may actually work.

This wouldn't affect sovereignty if the countries all agreed to practice it.

No. This hits on state and natl sovereignty which will not change.

Or it could be a consensual agreement between nations like marriage, driving rights, or any other number of things.

If the drugs you take are illegal in a country then don't go. Simple really.