Don't believe it? Remember RobertPaulsen? Look around.
The commerce clause has no doubt been stretched and abused all out of proportion to it's normal purpose, but the current war on drugs is rationalized using the commerce clause more because it's convenient to do so (after all, the precedent has already been established by the court) than because it is the more authoritative part of the constitution on the subject. I have long argued that the Defense clause is a more appropriate justification for the interdiction of internationally shipped poison into our cities. We would certainly not use commerce to justify stopping a Sarin gas attack, or an Anthrax attack, or a Dirty bomb attack, or a biological agent attack, we would see it as a rightful usage of the defense clause, and so too should we regard the interdiction of drugs as an appropriate usage of the defense clause.
The Chinese, the British, and the Japanese all regarded the importation of drugs into a nation as a weapon of war, and we are foolish if we do not so regard it as well.