SACRAMENTO, Calif. (AP) — The spiraling number of overdose deaths and hospitalizations among California prison inmates fell dramatically during the first two years of a program that uses prescribed drugs to treat more incarcerated addicts than any such program in the country, officials said Tuesday.

The rate of overdose deaths dropped 58% after the program began in 2020. Hospitalizations were 48% lower among those receiving the anti-craving drugs than among those waiting to begin treatment. The promising results show the program was effective even after accounting for restrictions during the coronavirus pandemic, according to doctors and researchers with the state corrections system and the federal official who oversees medical care in California prisons.

The report says the large scale results "are trending in a positive direction" and officials are "cautiously optimistic."

The findings come as Gov. Gavin Newsom's administration seeks $126.6 million in the next fiscal year and $162.5 million annually thereafter to expand treatment. The report said expanding the state's latest expensive attempt to curtail the prisons' pervasive drug problem is "at the highest priority level," given the impact on prisoner health, community safety upon inmates' release, and drug trafficking and violence it brings to prisons.

The state's approach includes the once-controversial step of using drugs including buprenorphine, naltrexone and methadone to dampen addicts' cravings and euphoria and relieve withdrawal symptoms while weening them off opioids. It took years of urging by lawmakers and treatment professionals for prison officials to try the program, although the approach is now widely used and has general support from California prosecutors and probation officers.

Early critics objected that the treatment substituted one drug for another, and that there could be a black market for some of the substitute drugs. In California, inmates are given the drugs in a sheet that dissolves under the tongue or by injection and are tested to make sure they are taking their medications.

More than 22,600 inmates have received the drugs and officials expect to eventually include 25,000 inmates annually, more than a quarter of the prison population. The program far exceeds the volume of treatments in any other U.S. correctional setting, California prison officials said.

In 2019, California's prison system had a record-high 51 overdose deaths per 100,000 inmates, more than double the overall death rate for other state prison systems. The death rate in California had been steadily climbing since 2012.

It fell to a rate of 21 deaths per 100,000 inmates in 2020 and to a preliminary estimate of 20 deaths per 100,000 inmates in 2021, with a final report on last year's deaths not expected until late this year.

Overdoses were the third-leading cause of death for California inmates before the program, but dropped to eighth in 2020, the lowest ranking in nine years.

"I'm not surprised at the results, because it's been proven to be an effective therapy that saves lives and reduces crime," said Don Specter, an attorney for inmates in some of the largest class-action lawsuits against the prison system.

J. Clark Kelso, the federal official who oversees inmate health, called the findings "a step in the right direction."

The results contrast with opioid deaths that increased across the U.S. as a whole. Driven largely by highly toxic fentanyl, overdose deaths rose from about 21,000 in 2010 to more than 100,000 last year.

Overdoses in California prisons began to drop about six months before the pandemic and continued after the department eased restrictions on visits and inmate movements, officials said. They said other state prison systems with similar pandemic restrictions did not see similar declines in overdose deaths and hospitalizations.

The results track earlier outcomes after prison officials began treating 60 inmates with medication in 2016.

Officials estimate that at least 65% of inmates have a substance abuse problem.

The use of anti-craving drugs is part of an approach that includes what is known as "cognitive behavioral therapy," in which people talk with mental health counselors to identify and change their own self-destructive behavior.

The program also aims to ease former drug users' transition back into the community, helping more than 2,200 parolees so far arrange continued treatment after their release.

Steven Fama, another attorney who represents inmates and tracks prison treatment programs, said corrections officials have slowly but steadily increased treatment and reduced the waitlist over the last two years, although there still are tens of thousands of inmates awaiting screening to see if they qualify.

Corrections officials said their goal is now to reduce the backlog, while developing therapy for inmates serving short sentences. They also aim to improve the handoff of parolees to community based treatment.