Health and Human Services Secretary Kathleen Sebelius. (Carolyn Kaster/AP)

The nation’s new health-care law says insurers can’t turn anyone away, even people who are sick. But some companies, patient advocates say, have found a way to discourage the chronically ill from enrolling in their plans: offer drug coverage too skimpy for those with expensive conditions.

Some plans sold on the online insurance exchanges, for instance, don’t cover key medications for HIV, or they require patients to pay as much as 50 percent of the cost per prescription in co-insurance — sometimes more than $1,000 a month.

“The fear is that they are putting discriminatory plan designs into place to try to deter certain people from enrolling by not covering the medications they need, or putting policies in place that make them jump through hoops to get care,” said John Peller, vice president of policy for the AIDS Foundation of Chicago.

As the details of the benefits offered by the new health-care plans become clear, patients with cancer, multiple sclerosis, rheumatoid arthritis and autoimmune diseases also are raising concerns, said Marc Boutin, executive vice president of the National Health Council, a coalition of advocacy groups for the chronically ill.

“The easiest way [for insurers] to identify a core group of people that is going to cost you a lot of money is to look at the medicines they need and the easiest way to make your plan less appealing is to put limitations on these products,” Boutin said.

ACA enrollment numbers, state-by-state

Insurers say that such accusations are unfounded, and that the drug coverage is more than adequate, with many plans exceeding the minimum levels required by the Affordable Care Act. But they acknowledge that to keep premiums low, they must restrict the use of some costly drugs if there are alternatives. And they say that when high-priced medications must be used, it’s reasonable to expect patients to pick up more of the cost.

Robert Zirkelbach, a spokesman for American’s Health Insurance Plans, an industry group, said the exchange plans are designed “to try to give consumers better value for their health-care dollars.”

Joanne Peters, a spokeswoman for the Department of Health and Human Services, said that the new health-care law will give many consumers access to the medicines they need for the first time but that if a plan doesn’t cover a particular drug, patients can ask insurers for an exception. She said the government is asking the companies to respond to such requests within three days.

The health-care law has been celebrated by people with serious illnesses, some of whom have been unable until now to obtain coverage. Starting Jan. 1, insurers must take all comers and are barred from imposing lifetime limits on reimbursements. For those who purchase on the marketplace, annual out-of-pocket costs will be limited to $6,350 for individuals and $12,700 for families. (The Obama administration granted a one-year grace period for some group plans to implement the new limit.)

But people who expected the new plans to provide pharmaceutical coverage comparable with that of employer-sponsored plans have been disappointed. In recent years, employers have compelled workers to pick up a growing share of the costs, especially for brand-name drugs. But insurers selling policies on the exchanges have pared their drug benefits significantly more, according to health advocates, patients and industry analysts. The plans are curbing their lists of covered drugs and limiting quantities, requiring prior authorizations and insisting on “fail first” or “step therapy” protocols that compel doctors to prescribe a certain drug first before moving on to another — even if it’s not the physician’s and patient’s drug of choice.

Paul Prince, 52, a former information technology manager from Houston, said he was surprised that some of the health plans in the new federal marketplace wouldn’t pay for one or more of his HIV medications. The policy that seemed to provide the best coverage, he said, would cover only about two-thirds of his monthly $2,400 drug tab, leaving him responsible for $840.

“There was no way I could pay that,” said Prince, who is studying to become a teacher after being laid off from his previous job and losing his insurance.

Prince receives help with buying his HIV medications from the government AIDS Drug Assistance Program for low-income people. But he worries about how he’s going to pay for his drugs when he goes back to work.

“I’m hoping the insurance companies will work this out by then, or else I will be in real trouble,” he said.

And there are fears that the government assistance programs, as well as those sponsored by foundations and drug companies, might be trimmed or eliminated on the premise that most Americans will have insurance — not taking into account that the coverage still will leave them with large bills for drugs.

The success of the health-care law hinges in large part on insurers being able to attract enough healthy people to help subsidize enrollees who are sick. Just 5 percent of the nation’s population — those with the most complex, chronic conditions — accounts for nearly half of all of U.S. health-care spending, according to the National Institute for Health Care Management, a research group funded by insurers. If insurers end up with a surplus of sick people, the result could be financially disastrous.

In the past, insurance companies could reject applicants who were sick — or had risk factors for becoming sick — or charge them higher premiums. The Affordable Care Act did away with that and left insurers with only a few ways to try to balance costs and risk. It allows them to charge more by age group (but the oldest group can be asked to pay only three times more than the youngest) and place of residence and if someone smokes.

But what is considered discriminatory in the design of drug benefits is less clear in the law and regulations issued by the Department of Health and Human Services.

The health-care law includes mechanisms to reimburse insurers for a portion of the costs for people with very high medical costs and to help carriers whose expenses may exceed the premiums they collect. But these are temporary measures, and insurers have complained that they are insufficient. HHS has said it is looking for ways to provide additional assistance if claims greatly exceed projections.

A new analysis of health plans sold in the federal exchange — which covers 36 states — and 14 state exchanges found that the benefits tend to be skimpier than in most other private insurance in the United States, with drug benefits a particular weak spot. The analysis, by Avalere Health, a health-care consulting company, was based on a sample of 600 insurance plans.

It showed that among “silver” plans — the second-cheapest of four levels of coverage in the exchanges, and the level on which federal subsidies are based — patients are required to pay a higher share of their drug costs than is typical among those who receive insurance through their jobs.

People who rely on extremely expensive drugs could encounter big bills right away. Patients whose medications cost at least $15,000 per month could face out-of-pocket costs of $1,000 to about $6,000 the first month they use their insurance, Avalere found. The analysis is based on the silver plans of the five states running their own marketplaces that have set their own benefits standards.

Dan Mendelson, Avalere’s chief executive, predicted that employers may soon adapt some of the benefit designs in the exchanges’ health plans. “We are already seeing interest,” he said, because they are less expensive for companies, shifting more of the expense to patients.

Daniel Kantor, a neurologist in Florida, said he has serious concerns about patients with multiple sclerosis who have purchased insurance through the exchanges, because some plans don’t cover widely used drugs. In addition, he said, some require doctors to prescribe a specified medicine before they cover others, which could compel people to take drugs more toxic to them, even though they are all similarly priced.

“2014 is going to be a scary year. People are going to have to stop taking medicines they are already stable on because of this,” said Kantor, the immediate past president of the Southern MS Consortium, a group of doctors, social workers and advocates who work with patients with the condition.

Insurers, he said, are hoping “that if they make it inconvenient for people with MS to get treatment, they will leave their rolls.”

Perhaps the most politically sensitive issue related to drug coverage involves people with HIV.

In an October letter to Health and Human Services Secretary Kathleen Sebelius, a coalition of AIDS groups voiced concern about the lack of coverage for a single-tablet regimen, in which three to four HIV medications are combined into one pill. Studies have shown that the tablets improve adherence to drug regimens and, as a result, reduce hospitalizations and enable people with HIV to stay healthier.

In reviewing health plans nationwide, the coalition found that at least 47 did not cover the single-tablet-regimen pills and other standard frontline treatments for HIV.

Robert Greenwald, director of the Center for Health Law and Policy Innovation at Harvard University, said some insurers are reconsidering their decisions and may begin covering the drug.

A spokeswoman for Aetna — which initially left the single-tablet regimen off the formulary, or list of medicine covered, for its exchange plans in at least eight states — has decided to add two of the three commonly used single-tablet regimens to all its plans. WellPoint BlueCross BlueShield said it will add one to its list of covered drugs in the 14 states where it has plans.

In Houston, three of the seven plans offered don’t cover single-tablet regimens and three others cover them only with very high coinsurance payments — as much as $1,200 a month — leaving what patients say is only one reasonable choice of carrier for those with HIV.

“We never expected these drugs to be completely left off some formularies,” said Randall Ellis, vice president of public affairs at Legacy Community Health Services, which treats 2,700 patients with HIV/AIDS. “It’s causing a lot of anxiety and confusion.”

Amy Goldstein and Lena H. Sun contributed to this report.