Actually, you do. However, manufacturing it, importing it, possessing it, appearing in public while under its influence, or engaging in commerce in it remain constitutionally prohibited.
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.