The companies reached an agreement in June 2012 in which Ameritox acknowledged several ads were false and agreed to no longer say its services could "confirm adherence" to prescriptions. The federal judge who approved the consent order agreement and dismissed the case expressed hope that would be the end of it.

The court "cautioned the parties that it had no intention of refereeing the advertising war that would likely follow" approval of the order, U.S. District Judge Benson Everett Legg wrote in a memorandum in January, as he dismissed related claims that had been rolled into the original lawsuit. "This proved a vain hope. Hostilities resumed within hours."

They have continued for years.

Since 2011, the companies have filed several lawsuits and countersuits in federal court involving disputes over patent infringement and unfair competition, some of which have been dismissed.

In one case that is still pending, Ameritox accused Millennium of providing kickbacks to labs in exchange for testing referrals. Millennium Vice President Martin Price said in an interview the company has never given kickbacks in exchange for referrals.

A case filed last month in Massachusetts federal court adds to the caseload.

In that lawsuit, Millennium accused Ameritox of funding lawsuits filed by former Millennium employees against it, as well as providing kickbacks to doctors in the form of free or discounted urine testing cups, dinners, computers and parties. Ameritox officials said they expect a judge to dismiss that case because a Florida court dismissed similar claims in a previous lawsuit.

Federal authorities in Massachusetts are meanwhile investigating Millennium, according to a November 2012 Reuters article. Proceedings of grand jury investigations are kept sealed, but some details came to light when former Millennium employees interviewed by investigators spoke with the news organization.

Price acknowledged the investigation but said company officials do not know what its focus is.

Officials from both Millennium and Ameritox said they are focused on preventing prescription drug abuse.

"The sad fact is that there is a national prescription drug abuse epidemic and scores of people are dying of overdoses every day," Ameritox spokesman Lon Wagner said. "So while Ameritox will continue to defend itself in court, we will remain focused on providing physicians with information to help them combat this epidemic."

Wagner said Millennium's lawsuits against Ameritox and several other competitors are a long-standing business tactic of the California company.

Millennium's Price said the same about Ameritox, and that its own lawsuits have been an effort to clean up an industry "rife with abuse."

"We feel like we're fending off Ameritox litigation and they'd rather fight in the courtroom than in the marketplace," Price said.

Opportunities for both companies and their competitors could be greatest in states like Kentucky, where laws passed in recent years require routine urine tests for those prescribed opioid pain relievers. Each test can cost several hundred to as much as $1,000, making the business a lucrative one, a fact not lost on Kentucky lawmakers.

"I need to go into the drug-screening business," Kentucky Rep. Stan Lee said jokingly in an interview with the Lexington Herald-Leader last year.

An earlier version had the wrong radio station for the Aches and Gains show. The Sun regrets the error.