NEW YORK, Sept 12 (Reuters) - As Michael Jackson's doctor, Conrad Murray, prepares for his involuntary manslaughter trial to begin in late September, he joins the small but growing ranks of healthcare providers facing criminal charges for their professional conduct.

Before the 1980s, the criminal prosecution of physicians for their healthcare decisions was virtually unknown. Between 1809 and 1981, there were only 15 reported appellate cases involving the criminal prosecution of doctors for malpractice, according to research by James Filkins, a doctor and lawyer who has written about the criminal prosecution of physicians.

Using the legal database Westlaw (a unit of Thomson Reuters), Filkins uncovered around two dozen cases from 1981 to 2001. For the period 2001 to 2011, the same search yielded 37 cases -- three times the rate for the prior two decades.

Drug Enforcement Administration data suggest a similar rise in prosecutions. For 2003, the agency reported 15 physician arrests that resulted in conviction; by 2008, the most recent year with comprehensive data, the number had grown to 43.

The growing numbers prompted the American Medical Association to adopt a resolution in 1995 opposing the "attempted criminalization of health care decision-making especially as represented by the current trend toward the criminalization of malpractice." The AMA said the trend interfered with the practice of medicine.

In the past decade, the majority of criminal cases against doctors have targeted the liberal prescription of painkillers and other controlled substances. Many of the cases are brought under the Controlled Substances Act, enacted in 1970, and similar state laws. To establish guilt under the act, the prosecution must prove that the physician knowingly and intentionally prescribed the medication outside "the usual course of professional practice" or not for a "legitimate medical purpose."

THE ANNA NICOLE SMITH CASE

The last much-publicized prosecution was of Anna Nicole Smith's physician, Sandeep Kapoor. He was charged with illegally providing Smith with an array of prescription drugs that led to the tabloid celebrity's overdose. That case, brought under a controlled substances law, hinged on whether Kapoor believed in good faith there was a medical purpose for the prescriptions, according to his lawyer Ellyn Garofalo. The jury acquitted Kapoor last year.

The difference in the Murray/Michael Jackson case is that California prosecutors are not charging Murray with violating a controlled substances law. That's because propofol, the anesthetic Murray is accused of giving to Jackson, is not a controlled substance. The drug, administered intravenously, is used to induce anesthesia and has rarely been abused as a narcotic. Prosecutors instead allege Murray breached the medical standard of care when he administered the anesthetic to Jackson at home, and that his gross negligence caused the singer's death at age 50. Murray faces up to four years in prison if convicted.

Murray is also facing a wrongful death lawsuit filed by Jackson's father ten months after prosecutors pressed criminal charges. The vast majority of medical malpractice cases are civil lawsuits filed by the victim or victim's family in which the penalty is monetary damages rather than prison time.

THE STANDARD DEVIATION?

The cost of defending a criminal case can be significant. In civil suits, doctors' legal bills are usually covered by their malpractice insurance plans, which don't extend to criminal charges. The AMA has argued that the civil tort system is sufficient for holding doctors accountable for negligent or incompetent actions.

The legal standards in civil and criminal negligence cases are similar. Both Jackson's family and prosecutors must prove that Murray deviated from accepted medical practices, though the standard for a criminal conviction is "much greater," than the one for civil cases, said attorney Ed Chernoff, who represents Murray.

Chernoff declined to discuss the Murray case specifically, but he is expected to argue that Michael Jackson was addicted to sedatives and painkillers and could have given himself the fatal dose of propofol when Murray was out of the room. Prosecutors will have to prove that Murray's conduct actually caused Jackson's death.

The Murray case unfolds against a backdrop of an epidemic in prescription-drug overdoses. From 1999 through 2006, the number of fatal overdoses due to prescription painkillers more than tripled nationally, from 4,000 to 13,800, according to 2009 data from the Centers for Disease Control and Prevention.

THE EPICENTER

Florida, which has earned a reputation as the epicenter of prescription drug abuse, has indicted dozens of doctors and clinic operators for unnecessarily prescribing pills. The governor and attorney general have launched a strike force to address the problem, and under new legislation, Florida doctors can no longer dispense pills at clinics, with certain exceptions for cancer and hospice patients. "Our marching orders are that we will not turn down a pill case coming into this office," said statewide prosecutor Nick Cox.

Critics say the scorched earth assault glosses over tough questions doctors face, especially physicians who treat chronic pain patients. Because pain is subjective, doctors must rely on the accounts of patients who are sometimes addicted and drug-seeking. "Doctors are not supposed to be law enforcement agents. They're supposed to believe their patients," said Diane Hoffmann, a law professor at the University of Maryland School of Law and an expert in health care law.

Murray's lawyer Chernoff said it is a mistake to criminally prosecute doctors who are not running pill mills but legitimately trying to help their patients. He blames the trend for having a "chilling effect" on the medical profession as doctors change their treatment plans out of fear of facing time in prison.

(Reporting by Terry Baynes)

(An earlier version misstated the name of the Drug Enforcement Administration.)