Washington - Many people in Medicare with diabetes, high blood pressure and other chronic conditions stop taking their medicine when faced with picking up the entire cost of their prescriptions, researchers say.

    About 3.4 million older and disabled people hit a gap, known as the doughnut hole, in their Medicare drug coverage in 2007. When that happened, they had to pay the entire costs of their medicine until they spent $3,850 out of pocket. Then, insurance coverage would kick in again.

    About 15 percent of those hitting the coverage gap stopped their treatment regimen. That rate varied depending upon illness. For example, about 10 percent of diabetes patients stopped buying the medicine, as did 16 percent of patients with high blood pressure and 18 percent of patients with osteoporosis.

    The drug benefit, which began in 2006, has come in under budget. Most participants report they are satisfied with the program. But many lawmakers and health analysts say improvements could be made.

    "If a new president and Congress consider changes to the drug benefit, it will be important to keep in mind that the coverage gap has consequences for some patients with serious health conditions," said Drew Altman, the chief executive officer and president of the Kaiser Family Foundation. The foundation conducted the study with researchers at Georgetown University and the University of Chicago.

    The Republican-led Congress in 2003 crafted the doughnut hole as a way to make the drug benefit more affordable for the federal government.

    The researchers based their findings on pharmacy claims data provided by IMS Health, a company specializing in collecting health care data. They excluded people who get extra help in paying for their drug coverage because of their income; they do not pay the full cost of medicine even when in the doughnut hole.

    When looking at spending by people who did not receive the extra help, researchers could determine when they hit the coverage gap, which began at $2,400 in total drug spending. They also could determine when they passed through the gap and catastrophic coverage kicked in.

    The researchers focused their analysis on eight categories of drugs. Those least likely to stop taking their medicine were Alzheimer's patients, at 8 percent. Those most likely, at 20 percent, were patients taking medicine for heartburn, ulcers and acid reflux disease, 20 percent.

    Jeff Nelligan, a spokesman for the Centers for Medicare and Medicaid Services, said the coverage gap kicks in after participants have saved about $1,600 on their drug costs, on average. He also noted that many plans offer some coverage when beneficiaries hit the doughnut hole. Those plans cost at little as $28.70 a month, and are available in every state for less than $50 a month.

    "We urge beneficiaries to choose wisely when selecting their drug coverage," Nelligan said. "Again, we emphasize that any changes to the coverage gap would need to come from Congress."

    The share of Medicare recipients who reached the doughnut hole varied widely by region. About one-third in Arkansas and seven states in the Northern Plains hit the coverage gap in 2007, but only 12 percent in Nevada did.

    Researchers said such regional differences may occur because of physicians' prescribing patterns as well as overall health of the population. A separate factor may be enrollment in Medicare Advantage plans. Such plans offer comprehensive health coverage on top of the drug benefit. Regions where Medicare Advantage plans were most prevalent had fewer enrollees hit the coverage gap, which could reflect stronger management of drug use.

    Democratic lawmakers have led efforts to let the government use its purchasing power to negotiate cheaper drug prices. They say the savings could be used to reduce the coverage gap, though the Congressional Budget Office projected that the legislation would not lead to any significant savings.

    About 5 percent of the people who hit the Medicare coverage gap switched to another medication, most often a generic drug, while 1 percent reduced the number of medications they were taking in a particular class of drugs, the report said.