Obamacare patients are discovering that many doctors, hospitals, and top cancer centers do not accept the plans they purchased.

“It’s so frustrating,” Terri Durheim of Enid, Okla., told CNN. “It’s not doing me a lot of good.”

Durheim is not alone. Obamacare’s so-called “narrow networks” are designed to limit customer choices to push patients into cheaper choices in an effort to control costs. Earlier this year Washington Post health writer Sarah Kliff warned that “Obamacare’s narrow networks are going to make people furious – but they might control costs.” A McKinsey and Co. study finds that more than one in three (38%) Obamacare plans permit patients to select from just 30% of the largest 20 hospitals in their geographic region.

For patients like Durheim, the reality of Obamacare’s slender options is forcing hard choices. Her son’s serious heart condition means she needs a pediatric cardiologist nearby. However, the nearest doctor her Obamacare plan covers is over an hour away.

“Obviously we’d have to pay out of pocket and go here in town, but that defeats the purpose of insurance,” says Durheim.

Cancer patients are also waking up to the realities of Obamacare’s narrow networks. According to an Associated Press analysis, only four of 19 nationally recognized comprehensive cancer centers offer Obamacare patients access to their facilities through all insurance plans in their state Obamacare exchanges.

“The challenges of this are going to become evident… as cancer cases start to arrive,” Executive Vice President of Seattle Cancer Care Alliance Norman Hubbard told NBC News.

As Obamacare customers learn that their access to doctors, hospitals, and top cancer centers have been severely curtailed, many are returning focus to promises President Barack Obama made that if you like your doctor, you can keep your doctor.

“If you like the doctor you have, you can keep your doctor,” Obama said.

Last week, however, Obama reversed himself on that promise during a WebMD interview.

“For the average person, many folks who don’t have health insurance initially, they’re going to have to make some choices, and they might end up having to switch doctors, in part because they’re saving money,” said Obama.