The Medical Board of California has launched an investigation into a string of 16 fatal overdoses tied to powerful narcotics prescribed by a prominent Orange County physician.

Dr. Van Vu, a pain management specialist in Huntington Beach, was featured in a Los Angeles Times article in November that detailed the 16 deaths.

A board investigator recently began obtaining signed releases from relatives of the deceased patients, authorizing the board to review their medical records.

"The wheels of justice grind slowly, but they grind," said Sally Finnila Sloane, whose brother Karl, 43, fatally overdosed on a cocktail of drugs in 2007, including two prescribed by Vu. "I was glad to see that somebody in charge was looking into this so it doesn't happen to anyone else."

IN DEPTH: Read the Times investigation

Charles Thurber, whose 22-year-old daughter Jennifer died of an overdose the same year, said he received a letter seeking permission to access her medical files.

She died after taking multiple drugs, including methadone and morphine prescribed by Vu, coroner's records show.

Thurber said he signed the form and sent it back to the medical board.

"It's definitely warranted," he said of the investigation.

Vu's attorney, Richard Wynn, said the doctor would cooperate fully with the investigation. He said Vu hopes that the medical board will form a committee to develop better protocols for treating chronic pain, and that he will be invited to participate.

"Dr. Vu is more than happy to assist in any way he can to make the system better," Wynn said. "We want not only to comply but to come up with a solution."

Fatal overdoses involving prescription painkillers and anti-anxiety drugs have risen sharply in the last decade, fueling a doubling of drug fatalities in the United States.

Authorities have focused on how addicts and dealers obtain such medications illegally, such as by robbing pharmacies or raiding family medicine cabinets.

A series of Times articles published last year showed that many patients overdose on medications obtained lawfully with a doctor's prescription. By studying coroners' records across Southern California, The Times identified 3,733 fatal overdoses from 2006 through 2011 and determined that nearly half stemmed from drugs prescribed for the deceased by a physician.

A small cluster of doctors — 71 out of tens of thousands practicing in Southern California — were associated with a disproportionate number of deaths. Each of those doctors lost three or more patients to overdoses. In each case, records show that medications prescribed by the physicians caused or contributed to the deaths. Vu was linked to more deaths than any other doctor, the Times analysis found,

Most of those doctors, including Vu, had clean records with the medical board, and there is no evidence that board officials knew about the deaths.

In interviews last year, Vu described himself as a conscientious, caring physician. He said patient confidentiality laws prevented him from discussing individual cases. But he said his practice includes many "very, very difficult patients" whose chronic pain often is complicated by substance abuse and depression, anxiety or other mental illness.

"I am doing the best I can in this very difficult field," he said. "I consider myself to be one of the best. But we have limits."

One of those limitations, he said, is his inability to control what patients do once they leave his office.

Vu said he was unaware of many of his patients' deaths and found the cases identified by The Times "eye-opening."