410 ILCS 620/3.14

Dispensing or causing to be dispensed a different drug in place of the drug or brand of drug ordered or prescribed without the express permission of the person ordering or prescribing. Except as set forth in Section 26 of the Pharmacy Practice Act, this Section does not prohibit the interchange of different brands of the same generically equivalent drug product, when the drug products are not required to bear the legend "Caution: Federal law prohibits dispensing without prescription", provided that the same dosage form is dispensed and there is no greater than 1% variance in the stated amount of each active ingredient of the drug products. A generic drug determined to be therapeutically equivalent by the United States Food and Drug Administration (FDA) shall be available for substitution in Illinois in accordance with this Act and the Pharmacy Practice Act.