Half of all the people arrested in Honolulu suffer from serious mental illness, severe substance abuse or both — a share that has doubled since 2010.

The number of psychologically troubled people placed in handcuffs is climbing despite a successful effort to funnel people who need mental health treatment toward hospitals and other care rather than arresting and locking them up.

“We’ve made good progress at diverting people from the criminal justice system,” said Honolulu Police Department psychologist Michael Christopher. “But we still arrest 2 people for every 1 we divert.”

Of the 10,824 people arrested in 2013 in Honolulu, 5,485 suffered from serious mental illness or severe substance intoxication, according to a review of records by the advanced practice registered nurses who work in the cellblock as part of the Honolulu Emergency Psychological Services and Jail Diversion Program. That fraction, 51 percent, has soared from 26 percent in 2010.

The jump in arrests of people with psychiatric and substance abuse problems followed substantial cuts to mental health care in 2009, including community-based services. And it tracks a mushrooming of the homeless population in Honolulu. Four out of 10 detainees at the downtown cellblock have no permanent home.

“So often people who are mentally ill are arrested because of the positive symptoms of their mental illness,” said Jerry Coffee, clinical director for the Institute for Human Services, the state’s oldest and largest homeless services provider.

“To an extent, in America we have kind of defaulted to manage our mentally ill population by putting them in jail,” he said. “You’re incarcerating somebody not because they had intent to break the law, but because they are incapacitated and broke.”

Across the country there are 10 times more people with serious mental illness in jails and prisons than there are in state psychiatric institutions, according to a survey published last year by the Treatment Advocacy Center, a national nonprofit.

In Honolulu the vast majority of arrests of people with mental illness or severe substance abuse in 2013 occurred without consulting a police psychologist beforehand, the Emergency Psychological Services program found in comparing pre-booking and post-booking records.

Some officers might disagree with the department’s policy of calling a police psychologist before arresting people they suspect are mentally ill. Or the arresting officer might not have witnessed active symptoms of mental illness.

In certain cases, police see little point in making referrals to police psychologists because they get frustrated by a revolving door, said Dr. Chad Koyanagi, a psychiatrist who cares for the most troubled street dwellers.

“As far as my interaction with police, their response is directly proportional to the amount of support they feel they have from community partners whose job it is to help mentally ill and homeless people,” Koyanagi said. “I think there are times when patients who are clearly ill, in distress, get brought to the hospital, and officers in their same shift later that day see the same people walking around. That’s demoralizing for the police.”

More than 40 percent of the arrests of mentally ill people are on warrants, largely for failing to appear in court for previous incidents, according to Christopher. Showing up in court — at the right place, at the right time and date — can be a major hurdle for people with mental illness. Most of the other arrests are for behavior that is directly attributable to their mental illness, he said.

“The seriously mentally ill are not the only population that is not receiving adequate health care in our society, but it is the only one that is being regularly arrested and incarcerated as a result of inadequate health care,” said Christopher, the HPD psychologist. “The reality is we’ve never invested anywhere near what we need to invest in health care for this population.”

Ultimately, some mentally ill people wind up spending more time in jail awaiting trial than if they had been convicted on the original charge — a burden to the individual, the correctional system and the state budget, Christopher said. Such arrests also contribute to overcrowding at the Hawaii State Hospital because detainees often arrive in court unfit to proceed and are sent there to be assessed.

Dr. James Westphal, chief of psychiatry at the Department of Health’s Adult Mental Health Division, said violence triggered by mental illness is actually quite rare and that the public overestimates the hazard. While people often fear strangers, they actually tend to be victimized by individuals they know, he said, noting that domestic violence is the leading cause of injury to women.

“According to the best research estimates, only approximately 4 percent of violence toward others in American society is attributable to mental illness,” Westphal said. “We’re talking about very small but unfortunately very publicized events.”

He added, “The mentally ill are much more likely to be a victim of violence than to perpetrate it.”

The stress of living without a home exacerbates underlying psychological problems that might be manageable in a stable environment. People with psychiatric problems who lack shelter face a bleak existence.

“Folks who have severe mental illness live in a consistently vulnerable state,” said Steven Balcom, crisis services coordinator with the Health Department’s Adult Mental Health Division. “Their income is very low, and once they fall into homelessness, it’s extraordinarily difficult to get them out, just from a resources perspective.”

“Oftentimes they get disconnected because their case manager can’t find them,” he said. “The good news is that as we continue to refine the data and information we have, we can find ways to use that information to help people get the services they need.”

The best way to minimize the risk of violence among the mentally ill, Westphal said, is “early detection and treatment, and intervention to assist with taking medication in the community.”

The Honolulu Emergency Services and Jail Diversion Program is stepping up training for police recruits in hopes of steering distraught individuals toward support rather than incarceration, without compromising public safety. Starting with the next class, recruits will receive 24 hours of training in mental health crisis intervention, up from three hours.