DENVER (AP) — They arrive before the sun, lining up for a lifeline that comes in a shot of pink liquid.

The doors to the methadone clinic on the campus of Denver Health open before dawn, and the line stretches down one side of the clinic hallway and back up the other. One at a time, patients swig a cup of methadone passed through an opening from the other side of a protective window.

The liquid opioid quenches the craving to shoot heroin and staves off a withdrawal that brings on vomiting, sweating, muscle aches and uncontrollable shaking in what some describe as the worst flu ever.

Denver Health's narcotic treatment program now has 550 patients, double what it had three years ago. But the medical center estimates it could serve four times as many people, more than 3,000, if it had the staff and other resources to take everyone addicted to opioids who walked in from the streets, visited the main hospital or was booked in the Denver jail.

It's a similar story across Colorado, where access to medication-assisted treatment for opioid addiction has expanded rapidly in the past few years but isn't yet close to getting a grip on the need, The Denver Post reported . Throughout the country, the epidemic has overwhelmed resources.

In the past three years, the number of methadone clinics in Colorado has doubled — from 11 to 23, in sync with a 2014 rule change that Medicaid would start reimbursing for methadone treatment. Most are in the Denver area, but there are now two in Pueblo and one each in the San Luis Valley, Colorado Springs, Greeley, Grand Junction, Montrose and Durango. New admissions to "opioid treatment programs" — the only places allowed under federal law to dispense methadone — have gone from 1,388 people statewide in 2013 to 3,566 last fiscal year.

Last week in Colorado, there were 5,100 methadone patients, according to a federal count. But the reach of opioid treatment programs — even as openings have picked up pace — hasn't been enough, when considering there are more than twice that many intravenous drug users in the Denver metro area, according to the Harm Reduction Action Center.

A recent Colorado Health Institute report found that of 22,000 people addicted to opioids in Colorado, just 4,000 received treatment at a clinic for opioid addiction.

At Denver Health, methadone the color of pink cough syrup flows from a tank, through a clear tube and into plastic cups, the dosage calibrated for each person. A few patients — 23 of the 550 — instead receive buprenorphine, another opioid-addiction drug that comes in a pill or a film that melts under the tongue. Patients must wait while it dissolves and then open their mouths to show a nurse it's gone.

About half the clinic's patients come every day to take their dosage in front of staff, while the rest are allowed to fill take-home prescriptions for the drugs used to treat addiction to heroin, painkillers and other opioids. Another section of the clinic — a secluded doctor's office separate from the walk-up windows — treats up to an additional 150 patients with prescriptions for buprenorphine.

Among those lined up outside each morning are people hoping to start treatment, desperate for help to kick heroin and already headed toward withdrawal because they know they can't start medication-assisted therapy if they are high. They're often referred by the city's needle-exchange program or staff at the public library. But only one, maybe two, will get in on any given day.

The same number are turned away.

"It happens every day," said Lisa Gawenus, manager of outpatient behavioral health services. One recently admitted patient was outside the building at 2 a.m., three hours before the doors open.

Doctors know those sent away might not end up at another methadone clinic in the city and instead will shoot up to avoid withdrawal. They hope they don't overdose before they return.

"These folks are really precious to us and we are losing a lot of people every day, unnecessarily," Gawenus said. "There are huge pockets of population we are not getting to."

While only highly regulated federal clinics can dispense methadone, physicians' offices can prescribe buprenorphine, also called by its brand name, Suboxone. Expanding availability of that drug is key in helping patients who won't go to a methadone clinic or those in rural areas where there is no opioid treatment program, state officials said.

Federal regulations require doctors to take eight hours of training, typically over two days, and limit doctors to 30 patients in their first year. A year ago, 270 doctors in Colorado were prescribing the drug, but since last April, the state Office of Behavioral Health has used grant funding to help register 235 doctors in the training, close to doubling the number who potentially can prescribe the drug.

Buprenorphine is often given to patients who are addicted to opioids but managing to maintain a job and somewhat stable life. For the sickest patients, the ones living day by day, doctors typically start with methadone. And for the most stable patients who can afford it, there is Vivitrol, a monthly injection that costs about $1,200.

Of the 64 counties in Colorado, 31 don't have a methadone clinic or a doctor who prescribes buprenorphine, according to a 2017 Colorado Health Institute report.

The difficulty in finding medication-assisted treatment is due in part to stigma, to the long-held feeling that substance abuse is a moral failing instead of a disease, said state health officials and other experts. It's a bias that prevents people from seeking treatment, but also one that has influenced regulation and insurance coverage that "historically has created barriers," said Marc Condojani, director of adult treatment and recovery at the state community behavioral health division.

It's especially frustrating, experts said, because medication-assisted treatment works — the risk of dying by overdose is reduced by half for patients who take the medication, studies have found.

Imagine if cancer or diabetes patients had to look as hard for a doctor who could prescribe them life-saving medication, said Cristen Bates, director of strategy, communications and policy for the office of behavioral health. "It would be a public health tragedy," she said. "It would be front-page news every day: 'Why aren't we getting people treatment?'

Medicaid only recently covered methadone, which is relatively cheap at $350 per month. The federal requirement for eight-hour training for buprenorphine has been another hurdle.

"Not once in medical school did I have to take a class that was eight hours dedicated to one specific medication," said Dr. Daniel Bebo, an addictionologist at UCHealth Center for Dependency, Addiction and Rehabilitation.

A general public perception is that recovering opioid addicts should wean themselves from the medication. But would doctors wean diabetics from insulin or tell them, "I've treated you three times and I'm done. You're not complying," Bebo asked.

"We don't get angry at grandma when she has an extra slice of cake and her blood sugar goes crazy."

Bebo works in a 30-day residential treatment center on the University of Colorado Anschutz Medical Campus in Aurora, where about one-fifth of patients are dealing with opioid addiction. He uses buprenorphine to help patients battle their cravings, and encourages them to continue taking it when they leave the program.

Medicaid will not pay for residential treatment, so patients pay out of pocket or use private insurance. A month-long stay is about $30,000.

"We're in the middle of a health care crisis and we've got empty beds," Bebo said. "That's the depressing part."

Denver Public Health director Dr. Bill Burman named expansion of medication-assisted treatment a top concern in fighting the opioid crisis. He described how treatment, ideally, should work: "The minute somebody says 'I'm ready,' you say 'great,' " he said.

The Colorado Coalition for the Homeless health clinic north of downtown could treat more patients with buprenorphine if it had an easier time hiring physicians and counselors, said Dr. Elizabeth Cookson, who directs the coalition's medication-assisted treatment program and is director of psychiatry.

The clinic, called the Stout Street Health Center, has 35 patients now on buprenorphine, and the waiting period to start treatment is usually one to three weeks. When coalition staff calls patients to book an appointment, they sometimes have changed their minds.

Ken Walker started methadone three years ago, arriving outside the Denver Health clinic at 3 a.m. knowing that if his life didn't change his "next stop was the grave."

He hadn't used heroin in 48 hours and was in "full-fledged withdrawal" — nausea, diarrhea, body aches. It was his second attempt at getting a walk-in spot; the first time he had arrived at 5:30 a.m. and already five people were waiting.

But on this day, when the clinic would accept only one new person, the couple ahead of him let Walker go first. "Honestly, I think they just saw I was broken," he recalled.

Walker, who first used opiate painkillers as a teenager after a friend had stolen them from his mother, was using intravenous heroin and living on Denver streets when he took his first dose of methadone. He went back every morning for weeks.

Now, three years later, Walker, 35, gets a two-week prescription, one small bottle per day to drink at home. He has an apartment, is a manager of a convenience store and has reconnected with his relatives. He recently took a job as a peer mentor for Denver Health patients addicted to opioids.

"My life is actually very good," he said.

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Information from: The Denver Post, http://www.denverpost.com