Two medical doctors are among the five people charged in connection with "Friends" star Matthew Perry's death, officials announced Thursday.

Perry, 54, was found unresponsive in his pool last year and the Los Angeles County Medical Examiner's Office said his death was caused by "the acute effects of ketamine."

While not unheard of, experts told USA TODAY it's relatively rare for physicians to be criminally charged in overdose cases given the huge number of doctors in the U.S., and most of the cases where charges are brought relate to the ongoing opioid crisis.

"This is an exceptional and tragic case," said Dr. Caleb Alexander, a professor at the Johns Hopkins Bloomberg School of Public Health.

Southern California doctors Salvador Plasencia and Mark Chavez are both accused of conspiring to distribute ketamine to Perry, and deliberately fueling his addiction in order to gain profit for themselves, prosecutors said. Three other people are also charged: Jasveen Sangha, also known as "The Ketamine Queen" of North Hollywood; Perry's live-in assistant Kenneth Iwamasa; and Eric Fleming, who admitted to distributing the ketamine that killed Perry.

What are the doctors accused of?

The two doctors played an integral role in Perry's untimely death, and "took advantage" of Perry's known struggle with drug addiction to make a profit, U.S. Attorney Martin Estrada said at a news conference.

Plasencia, 42, is charged with one count of conspiracy to distribute ketamine, seven counts of distributing ketamine and two counts of falsifying records.

Chavez, a 54-year-old doctor from San Diego, agreed to plead guilty to one count of conspiracy to distribute ketamine. Prosecutors say he sold the drug to Plasencia and submitted a fake prescription in the name of another unsuspecting patient to access more vials of ketamine that he could sell to Plasencia, for distribution to Perry.

According to prosecutors, Plasencia, who is from Santa Monica, learned that Perry wanted to purchase ketamine – which is most often used as an anesthetic and requires close monitoring – and coordinated with Chavez to obtain large amounts of the drug. Plasencia met with Perry and his assistant Iwamasa and taught them how to inject Perry with the drug, they said. Plasencia also injected the drug into Perry himself, including once inside a parked car, prosecutors said.

"I wonder how much this moron will pay," Plasencia said in a message to Chavez, according to an indictment.

Plasencia continued to sell the ketamine to Perry even after he learned Perry's addiction was "spiraling out of control," prosecutors said.

“Dr. Plascencia and Dr. Chavez violated the oath they took to care for their patients. Instead of 'do no harm,' they did harm so that they could make more money," said Anne Milgram, administrator of the Drug Enforcement Administration.

How common is it for doctors to face charges?

The charges bring to mind the case of Dr. Conrad Murray, Michael Jackson's personal physician who was found guilty of involuntary manslaughter after the singer's 2009 death from a fatal dose of the drug propofol.

But the majority of charges related to drug overdoses are brought against doctors who treated everyday Americans, not celebrities, said Adam Gershowitz, a professor at William & Mary Law School, who has published research on doctors convicted for prescribing opioids for illegitimate medical purposes. Still, a high-profile death can motivate prosecutors to conduct a thorough investigation.

"Generally speaking, these are cases where the U.S. Attorney's Office has begun investigating, not because anybody famous died, but because ... they have been in the business of prosecuting doctors for these illicit drug sales and for deaths that occur during them," Gershowitz said.

Overall, criminal charges against doctors are rare, and the vast majority of them are tied to opioid overdoses, which have led to a crackdown on physicians overprescribing, all while illegally manufactured fentanyl has taken over drug sales on the streets.

More than 4,200 doctors have faced criminal drug-related charges since 2014, around the time when illegally manufactured fentanyl entered the scene in the U.S., fueling tens of thousands of opioid deaths annually. That's according to an analysis of data from the National Practitioner Data Bank by Tony Yang, a professor and associate dean for health policy and population science at the George Washington University School of Nursing.

Over the last few years, the number of doctors charged has dropped, Yang told USA TODAY. The DEA took action against 479 doctors in 2016. In 2021, the number had dropped to 447 and steadily fell to 391 in 2022 and 330 in 2023.

In 2015, Southern California Dr. Hsiu Ying “Lisa” Tseng, became the first physician in the U.S. to be convicted of murder for prescribing the drugs that led the fatal overdoses of three patients. Other cases include Dr. Martin Tesher, who was convicted of distributing oxycodone without a legitimate medical reason in Brooklyn in 2017, leading to a fatal overdose. A Manhattan doctor, Gordon Freedman, was sentenced to more than 17 years in prison in 2021 for drug charges, including distributing oxycodone and fentanyl without a medical reason to a patient who also died.

The legal challenges of prosecuting a doctor

When prosecutors decide to charge medical doctors with drug charges, they have to not only prove the doctor distributed the drugs, but also that there was no legitimate medical reason to do so. That's a high burden of proof that can be tricky to prove beyond a reasonable doubt, said Gershowitz, because doctors are often able to say prescriptions were related to symptoms the patient expressed. Many times, a doctor might have their medical license suspended or taken, but not face criminal charges, he said.

Charges tend to be brought only in cases involving more egregious conduct, Alexander said. That could include a doctor who sees dozens of patients in a day and does not spend enough time to properly evaluate them but still prescribes dangerous drugs; exchanges large amounts of cash during an office visit; or keeps shoddy records.

Nassau County, New York, doctor George Blatti, for example, was sentenced to up to 15 years in prison earlier this year for second-degree manslaughter after his overprescription of opioids led to five deaths. Prosecutors said he prescribed massive amounts of pills to patients, including some he had never examined or even met. He met patients in his car and wrote prescriptions while parked at the hotel where he lived or at a nearby Dunkin' Donuts.

Ketamine is a bit different than the opioid cases, Alexander said. While opioids have a wide range of appropriate uses and reasons to be prescribed, ketamine is almost exclusively used in the administration of anesthesia, he said. Its primary effect is to alter someone's state of consciousness, mood, behavior and cognition.

Alexander said the charges against the doctors who allegedly distributed ketamine to Perry are important.

"These cases serve two purposes: the first is that a well functioning legal system requires that individuals be held accountable," he said. "And it's also important to the degree that it deters others from wandering beyond reasonable standards of care."