The commerce clause should allow the Federal government to step in and settle disputes between the States about commerce in goods such as Marijuana, but it shouldn’t give them the power to flat-out ban it nationwide. For example, if Oregon has banned it, but California continues to illicitly import it into that state, the Federal government could use the commerce clause to step in and put a stop to that.
Yet it is very certain that it grew out of the abuse of the power by the importing States in taxing the non-importing, and was intended as a negative and preventive provision against injustice among the States themselves, rather than as a power to be used for the positive purposes of the General Government, in which alone, however, the remedial power could be lodged.
http://press-pubs.uchicago.edu/founders/documents/a1_8_3_commerces19.html