He began his career in 1972 at Invenex Pharmaceutical on Grand Island, NY. He worked his way up at LyphoMed.
In October 2017, Kapoor was arrested in Arizona and charged with RICO conspiracy, conspiracy to commit wirefraud, and conspiracy to violate the Anti-Kickback Law. The charges stem from allegations he participated in a scheme to bribe doctors to prescribe a fentanyl-based cancer pain drug, an addictive synthetic opioid. U.S. Attorney william Weinreb said the charges reflected authorities' commitment to combat the opioid epidemic. Kapoor is also alleged to have conspired to defraud health insurance providers. Shortly after the charges were announced, Kapoor resigned from the Board of Insys Therapeutics.