Over the two and a half years following the 2022 rollout of the 988 national suicide prevention hotline, the rate of suicides among young people in the United States dropped 11 percent below projections, decreasing most sharply in states with a higher volume of answered 988 calls, a new study has found.

The findings, published today as a research letter in JAMA, compared suicide deaths from July 2022 to December 2024 with sophisticated mathematical projections that were based on historical trends. This yielded good news, with 4,372 fewer suicides of adolescents and young adults, ages 15 to 34, than had been projected.

To ensure that the decline was related to the use of the hotline, researchers at Harvard Medical School teased out the trends in states with high and low usage of the hotline. The findings were striking: The 10 states with the largest increases in 988 calls experienced an 18.2 percent reduction in observed suicides compared with expected suicides; in the 10 states with the lowest uptake, the reduction was smaller, 10.6 percent.

The results suggest that the government’s investment in the 988 rollout has translated into “a measurable reduction of deaths,” said Dr. Vishal Patel, a resident physician at Brigham and Women’s Hospital and one of the authors of the study.

“What our study has added,” he said, “is evidence for the deeper benefit of the program, and that is, that at the population level, among young people at least, suicide mortality is lower than it would have been without the program.”

He added, “The implication of that is that sustained funding for this program matters.”

The United States rolled out the three-digit hotline with bipartisan support in July 2022, replacing a 10-digit hotline number, and augmented it with a $1.5 billion investment in crisis center capacity. Since its inception, the service has fielded more than 25 million contacts, according to the Department of Health and Human Services. The agency has asked Congress for $534.6 million to fund the program for 2027.

Last summer, the Trump administration terminated one element of the hotline, the Press 3 option for L.G.B.T.Q.+ callers. The Substance Abuse and Mental Health Services Administration said that the Press 3 option was being discontinued because it had exhausted its funding from Congress and that the hotline would “focus on serving all help seekers.”

But advocacy groups and policymakers protested the decision, and in testimony before the Senate on Tuesday, the health secretary, Robert F. Kennedy Jr., said his agency was planning to restore the Press 3 option.

Dr. Patel said his group had become curious about measuring the program’s effectiveness after Press 3 was eliminated. While call volume and satisfaction surveys suggested that 988 was succeeding, he said, the harder question was, “Did the creation of this 988 program, the transition from the old hotline to this hotline, actually move the needle on suicide mortality?”

Experts said it was difficult to tease out the beneficial effect of 988 from other things that changed in 2022, the year that the new hotline was created. Around that time, suicide prevention programs were being introduced in schools, in faith communities and on social media, but more important, the pandemic was ending.

“We were finally out of this crazy time, and there was a sense of optimism and hope,” said Jonathan B. Singer, a professor of social work at Loyola University Chicago and a co-author of “Suicide in Schools.” He called the downward trend in youth suicides “encouraging, but it is tempered by the fact that we don’t have a good explanation as to why.”

The authors acknowledged that their findings could not account for the influence of social and economic changes, changes in mental health services or public awareness about services.

But they did make comparisons to exclude other possible explanations. The authors looked for similar effects among American adults over 65, who are less likely to use the hotline. In that group, there was a reduction in suicides that exceeded expectations, but it was smaller, at just 4.5 percent.

To ensure the decline in suicides did not reflect a general improvement in young-adult mortality, the researchers tracked cancer deaths, and found there was no change. They also looked at the rates of suicide among young people in England, where no change had been made to the national crisis line in that time period; they found no reduction in youth suicides there.

Hannah Wesolowski, chief advocacy officer for the National Alliance on Mental Illness, said she was persuaded that the hotline had contributed to the improvement in suicide rates, in part because it did not appear among English youths or in older Americans.

“To me, that really helps hone in that this might really be the differentiator,” she said. “We are seeing potentially a pretty significant decline in suicides among young people. For public policy, this is strong evidence to double down on that we are doing.”

Emily Hilliard, a senior press secretary at the Department of Health and Human Services, said H.H.S. and SAMHSA are “committed to ensuring that all Americans have access” the 988 line, which she said “clearly provides lifesaving support, helping millions of people every year.”

If you are having thoughts of suicide, call or text 988 to reach the 988 Suicide and Crisis Lifeline or go to SpeakingOfSuicide.com/resources for a list of additional resources.