Complex sentence: While originally intended to regulate the trade, it soon became a prohibitive law, eventually becoming legal precedent that any prescription for a narcotic given by a physician or pharmacist--even in the course of medical treatment for addiction--constituted conspiracy to violate the Harrison Act.
Split into simpler sentences: While originally intended to regulate the trade, it soon became a prohibitive law. It soon became legal precedent that any prescription for a narcotic given by a physician or pharmacist--even in the course of medical treatment for addiction--constituted conspiracy to violate the Harrison Act.