A lawyer for Insys declined to comment beyond a brief statement that said the company was cooperating with authorities “in all relevant investigations.” Lawyers for Mr. Babich and Alec Burlakoff, who was the company’s vice president of sales, said their clients would plead not guilty. Anthony Pacheco, a lawyer for Joseph A. Rowan, a former regional sales director, described the indictment as a list of “the government’s unproven factual assertions and legal theories.” Lawyers for the other defendants either did not return calls or could not be reached.

Prosecutors said executives at Insys began to aggressively market Subsys soon after it arrived on the market in 2012, and they were frustrated because it was not performing well against several similar fentanyl products that were already on the market. So over the next few years, they set out to woo pain doctors who had a track record for prescribing large quantities of fentanyl, enticing them with speakers’ fees, lavish dinners and in some cases going so far as to hire their relatives.

In one exchange, Mr. Burlakoff texted a sales representative and told her not to worry about whether one of the doctors had good communications skills. “They do not need to be good speakers, they need to write a lot of” prescriptions for Subsys, he told her, according to the indictment.

In return, the indictment said, the doctors wrote large numbers of prescriptions for people who did not have cancer. An analysis in 2014 showed that only 1 percent of prescriptions for the drug were written by oncologists.

Top prescribers were given special treatment, with Insys assigning its own employees to help with office work. In the case of one high-prescribing doctor in Alabama, the indictment said, the company dedicated a sales representative to attend to all of his needs. After the doctor became a paid speaker for Insys, he went from writing about two prescriptions a week to about 11 prescriptions a week, prosecutors said.