A tax is imposed on marijuana and controlled substances as defined in Code Section 48-15-2 at the following rates:

(1) On each gram of marijuana, or each portion of a gram, $3.50;

(2) On each gram of controlled substance, or portion of a gram, $200.00; and

(3) On each ten dosage units of a controlled substance that is not sold by weight, or portion thereof, $400.00.