Sorry for the confusion guys. It wasn't the question, which is indeed legitimate and should be answered. The first answer however contained some advice that might be seen as encouragement to use drugs in SEA (and not just opium). That has been removed from the post and my answer hopefully will avoid people posting such advice again.
Incidentally, the possession or trafficking of drugs in Vietnam is most certainly very illegal. As this article mentions, about 100 people each year are sentenced to death for drug related offences.
Opium is however much more readily available in Laos, though as this article points out, it is still an illegal activity and as such certainly shouldn't be encouraged on these forums.
As for Thailand, well, that wasn't really in the question.