Lauren Stevens, former associate general counsel at GlaxoSmithKline, fought the criminal justice system last year and won. She gave her first major public talk on the ordeal Monday, offering up hard-learned lessons to other in-house counsel at the annual meeting of the Association of Corporation Counsel in Orlando.

Amar Sarwal, chief legal strategist at ACC, introduced Stevens by warning the 1,600 in-house bar members that “the government and prosecutors have a target on your back.”

But she had a gentler take on it all, saying, “You can’t go through something like this without being changed, and for the better.”

Stevens, now retired, was acquitted of criminal charges in May 2011. She was accused of obstructing a U.S. Food and Drug Administration inquiry into off-label drug marketing at GSK, allegedly by making false statements and by withholding information that was requested but not subpoenaed.

But in a strongly worded decision, the federal judge summarily threw out the prosecution’s case in mid-trial—indicating that Stevens never should have been charged, and that attorney-client privileged documents never should have been turned over to the prosecution.

Stevens walked the audience step-by-step through her experience of the case.

It began in 2002 when she was “working in the trenches” in the legal department at the drug giant in Raleigh-Durham, N.C. Her boss asked her to handle a letter the company had received from the FDA.

The letter asked questions about possible off-label marketing of the drug Wellbutrin. In all, the FDA sent seven letters on the topic, she said.

The first letter was unusual, Stevens said, because it read like a subpoena but it wasn’t. The FDA was seeking voluntary compliance—and GSK agreed to cooperate.

Stevens said she put together a legal team that included in-house lawyers plus outside counsel from King & Spalding. After 13 months of employee interviews and document research, the team presented its conclusions.

“We discovered the company had no intent to market this drug off-label,” Stevens said. “But of course mistakes were made, and we disclosed them quickly to the FDA and rectified them, and put in place structures to keep those issues from happening in the future.”

Outside counsel drafted the responses, Stevens said, but she signed them because GSK was afraid that if “we fronted the law firm to the FDA, it would raise a red flag.”

Today, she noted, nearly every company hires outside counsel when it’s dealing with an inquiry from a government regulator. She drew laughs when she said that’s the first lesson she learned, “If you’re going to write letters to agencies, have your outside counsel sign them.”

But what Stevens didn’t know at the time was that the U.S. Department of Justice was looking into other alleged marketing misconduct at GSK over eight drugs, and only one was Wellbutrin. Prosecutors asked the FDA to turn the Wellbutrin probe over to them.

In 2007, after Stevens spent several years trying to please the FDA, her boss came into her office and said, “We need to hire an attorney to represent you. DOJ has concerns about false statements in documents you sent to the FDA.”

Stevens said she wasn’t worried because she knew any criminal charges would require intent on her part to commit a crime, and she had none. But she hired Brien O’Connor of Ropes & Gray in Boston anyway.

Two years later, in 2009, DOJ finally issued a target letter against her and she added a second law firm, Steptoe & Johnson based in Washington D.C., to the defense team. GSK paid her legal team—she didn’t know how much—and gave her administrative leave so she could focus on her defense.

In May 2010 she was indicted, arraigned, fingerprinted and photographed for a mugshot. “And this nice jailer asks, in all seriousness, ‘This isn’t going to ruin your legal career, is it?’ “

During the trial, her defense team painted her as an honest but zealous advocate for her company. After the prosecution had rested its case but before the defense began, one of her attorneys asked for a dismissal because the government hadn’t proven a crime was committed.

“My attorney said, ‘Don’t get your hopes up; this never happens,’ ” she said.

But this time it did.

She remembers going to court that morning and “I am absolutely frozen in my chair as [the judge] talks … I’m holding my breath and I didn’t even hear what he said.” What he said was: case dismissed, with prejudice.

Stevens told the lunchtime crowd at ACC that she and her legal team walked back to their hotel, “and the sky is the bluest I’ve ever seen it.” It was only 10:30 in the morning, but one of her attorneys asked the hotel to open the bar, and they did. “The rest of the day,” she quipped, “is a blur.”

Today, Stevens said she is consulting for GSK—and loving it—while still enjoying her retirement by biking, gardening and hiking.

Among the lessons she emphasized for other in-house counsel:

• “The use of outside counsel was absolutely critical. Be sure it’s someone who will be there for you six or seven years later.”

• Take careful notes of meetings, and be careful with emails because they may get admitted into evidence one day. “This isn’t a lesson about don’t take notes, but about take effective notes. … Had we not had those notes I wouldn’t have remembered all those [exculpatory] things we did back in 2003.”

• Don’t make your legal arguments in your letters to agencies. She recalled that her letters to the FDA contained “a lot of advocacy and zealous representation. If I were to do it again, I think I would set a different tone in the letters.”

• Finally, don’t be afraid to go back to work and practice law with a passion. “That is what you do—go back and defend your client zealously and don’t back away because you are afraid of my experience.”