I would agree that the feds have the authority to prohibit the importation of cocaine, as that is an issue regarding our borders.
Now, here is a thornier issue - where does the federal government get the Constitutional authority to prohibit someone from growing a pot plant in their home for their own consuption. Hint: No commerce is involved and the pot does not cross state borders. And if you resort to Wickard to justify the feds prohibiting such, may you be sewn into a sack with Helen Thomas and thrown on a waterbed.
They don't. Only the states have that authority. That's why the 18th Amendment was needed to permit the feds to prohibit personal consumption of alcohol. Now getting the courts to agree with that interpretation is a different story.