A tax is imposed on marijuana and controlled substances as defined in Section 12-21-5020 at the following rate:
(1) on each gram of marijuana, or portion of a gram, three dollars fifty cents;
(2) on each gram of controlled substance, or portion of a gram, two hundred dollars;
(3) on each fifty dosage units of a controlled substance that is not sold by weight, or portion of fifty dosage units, two thousand dollars.