For millions of people, Obamacare offered an opportunity to finally get insurance coverage for pricey medications that they were forced to pay for out of pocket—or were unable to buy at all—in the past.
But experts say that while the Affordable Care Act has been a net positive when it comes to reducing the financial burden of prescription drug costs, it is not a cure-all. Often people are surprised about how much they personally owe, even under their new form of insurance.
Many times the realization comes at the pharmacy counter when patients try to fill their prescriptions, according to Karen Pollitz, a senior fellow at the Kaiser Family Foundation.
"It's just a heck of a way to find out what your insurance does and does not cover," Pollitz said.
She added, "They won't let you leave a CVS counter by just leaving an IOU. They want you to pay there."
And trying to avoid sticker shock at the drugstore and reduce out-of-pocket expenses when shopping for an insurance plan is no easy feat.
Under the health-reform law, prescribed medications are one of the 10 "essential benefits" that must be covered by individual and small-group insurance plans. Those plans must cover at least one drug in a given class or category, and each plan in a given state region must offer the same number of drugs as is offered by a benchmark, or minimum plan.
The ACA also caps the out-of-pocket costs a person must pay for their in-network medical treatment at $6,350 per individual, and $12,700 for a family, meaning that if they buy medication included in the plan's benefit package, they will not owe more than that sum each year.
But figuring out what drugs are included in a plan's formulary, or list of covered medications, can be tricky for new insurance customers, according to experts.
One complicating factor is the use of so-called cost-sharing tiers for covered medications. Tiers break up covered drugs into different categories, with patients responsible for lower co-payments and co-insurance costs in the lower tiers, and higher costs in the higher tiers.
But knowing which drug falls into which tier is difficult, and it makes it difficult for most shoppers to figure out which plan will cost you more. And that is assuming you have a good sense of what your needs will be. In some cases, it may be literally "impossible," a recent analysis found.
Julie Huppert, vice president of health-care reform at Express Scripts, said the insurance terms such as co-payment, co-insurance and deductible "will be foreign" to many new Obamacare enrollees, who may not have had insurance in the past.
And those terms "will cause some surprises for them," Huppert said, because they will in some cases lead to people owing much more in out-of-pocket costs than they would have imagined when they signed up for their new insurance plan.
Huppert said that in addition to confusion about what is legitimately owned by patients for medications, there will be errors in cost calculations and determinations of what drugs are covered in the new Obamacare exchange-sold plans.
That means that "in this first year, we'll probably have a lot more stories about what went wrong than what went right," Huppert said.
The ACA reforms came too late for Pat Raia, a freelance writer from Florida, who incurred more than $100,000 in out-of-pocket costs for treatment after she was diagnosed with breast cancer in 2012.
Although she had an individual insurance plan, Raia was forced to foot her cancer-related bills herself after her insurer argued that her cancer was pre-existing, and hence not covered by the plan. The scenario would not occur today under ACA because most individual plans are now barred from denying people coverage for pre-existing conditions.
Raia, 60, said she had to pay $7,200 just for the chemotherapy drugs that helped put her cancer in remission. And she still has not paid off about $75,000 in total medical debt related to her cancer.
As a result, when she shopped for Obamacare plans on HealthCare.gov, she paid close attention to whether they drugs she used where in the formulary.
"I was looking at drugs I might need in the future, because you never know," Raia said. "They're covered."
Raia said Obamacare plans will be "beyond helpful" for someone who is diagnosed with cancer or another serious illness, and faces the need for expensive medication.
"I didn't sleep at night thinking about the costs of these bills," she said.
Kirsten Sloan, senior policy director of the American Cancer Society's Cancer Action Network, noted that it's not unusual for cancer patients to need medication that can costs tens of thousands of dollars per year, if not more, and "you can be talking about a treatment window that's anywhere from one year to seven years."
Pre-Obamacare individual plans weren't obligated to cap out-of-pocket costs for those plans. And in many cases, people with a diagnosis of cancer either couldn't obtain insurance or had plans that didn't come close to covering their medical needs.
With Obamacare, "cancer patients are in a much better position than they were originally," said Laura Skopec, a senior analyst at the Cancer Action Network.
A recent analysis by Skopec and Sloan looked at the availability of 14 cancer drugs in 62 Obamacare plans offered in five states and the District of Columbia. They found that coverage for those drugs was "fairly comprehensive across plans."
But how the plans are designed to share the costs with patients for the drugs "vary widely," the analysis found.
"We definitely see plans on the marketplace that use co-insurance for these specialty drugs," Skopec said.
This means patients taking such drugs "are seeing co-insurance rates of up to 50 percent, and that's on their first visit to the pharmacy," she said.
And even with the cap on out-of-pocket costs, those kind of cost-sharing rates can put a strain on people's wallets.
Given that, the analysis said, "It is critical for patients to be able to access and easily compare coverage and cost-sharing designs."
"We found, however, that cancer patients would face a difficult, and in some cases impossible, task in making apples-to-apples comparison of health plans based on drug coverage," Sloan and Skopec wrote.
That's because, among other things, there is no consistency in how plans provide direct links to their drug formularies. Some plans may even lack a comprehensive list of the covered drugs, and the formularies are not organized in the same way, the analysis found.
"The transparency issue is significant, because a person with cancer needs to be able to know that the drugs that they're taking are on their formulary," Sloan said.
While Obamacare plans cover more drugs for more people than in the past, not everything is covered. If drugs aren't included in a formulary, but you need them, "then you're on your own" in terms of paying for the medication, said Kaiser's Pollitz.
The ACA does establish a external review process in which a patient who claims the drugs are medically necessary can argue they should be covered by insurance. But there is no guarantee they would win, or that they would not first incur steep bills first.
—By CNBC's Dan Mangan.