In March of 2013, Gordon Freedman, a doctor on Manhattan’s Upper East Side, fielded a request from a regional sales manager for the manufacturer of Subsys, a spray form of the highly addictive painkiller fentanyl.

Dr. Freedman was already a top prescriber of Subsys and also one of the company’s paid promotional speakers. Now the sales manager was telling him the company, Insys Therapeutics, would increase the amount of money it was paying him and asked that he increase the number of new patients he was prescribing Subsys.

“Got it,” Dr. Freedman replied, according to authorities. By 2014, they said, Dr. Freedman had become one of the country’s top prescribers of the painkiller drug — and also the company’s highest-paid speaker.

The exchange between the doctor and Insys was detailed in a federal indictment unsealed on Friday in Manhattan, charging Dr. Freedman, of Mount Kisco, N.Y., and four other New York doctors with participating in a bribery and kickback scheme that prosecutors said sought to increase the drug company’s sales and preyed on unwitting patients.