Not according to every federal court that ruled on it. Who told you it was unconstitutional? Who lied to you?
The Constitution contains no provision for banning anything. A special amendment had to be added to ban alcohol. When the ban on alcohol was lifted the amendment had to be repealed.
Where is the Constitutional Amendment for the ban on marijuana?
If you have proof to the contrary, post it! Cite the Constitutional clause that gives the power to ban only, please.
And forget the commerce clause, the government didn't use that to ban alcohol. Remember, a special amendment was needed.