More than 80 percent of those enrolled in Medicare drug plans are satisfied with their choice, although fewer than half of the beneficiaries report saving any money, a survey says.

Almost two in 10 people, or 18 percent, reported major problems with their plans, according to Thursday’s survey. It was the latest in a series of surveys on the drug benefit by the Kaiser Family Foundation of Menlo Park, Calif.

Problems reported by people 65 and older included unexpected costs, inability to get prescriptions filled immediately and having to switch drugs.

More worrisome was that 27 percent of older people in fair or poor health reported experiencing major problems, compared with 12 percent of those in excellent or very good health, said Drew Altman, the health research foundation’s president and chief executive.

The poor, along with people who take six or more prescription drugs a day, also reported higher rates of problems with the program.

"It’s certainly not the catastrophe many critics had predicted it would be, but there definitely are significant problems," Altman said.

"When beneficiaries who are the sickest, poorest and use the most drugs are most likely to have the most problems, that’s the opposite of what we would like to see," he said.

The foundation interviewed 1,585 people in English and Spanish, including 509 in Medicare drug plans, between June 8 and June 18.

The survey found that 81 percent were either very or somewhat satisfied with their plan. Also, 46 percent reported saving money on their prescription drugs. One in three said they were paying the same, while one in six said they were paying more.

Medicare’s chief said experience with the program will allow the government and the companies behind the plans to offer beneficiaries more help next year.

"We have learned a lot about what people want in their drug coverage," said Dr. Mark McClellan, administrator for the Centers for Medicare and Medicaid Services. "That’s going to be reflected in choices that are simpler."

The latest survey results closely match the findings of an AARP survey in May, said Steve Hahn, a spokesman for the advocacy group.

Medicare data show that the complaint rate has dropped since the program began in January and is now at two per 1,000 beneficiaries, McClellan said. The Kaiser survey suggested 55 percent of major problems and 90 percent of minor" problems were resolved satisfactorily.

The margin of error for the Kaiser survey was plus or minus 3 percentage points for all people, and 4 percentage points for those enrolled in Medicare drug plans.

The government estimates that about 38.2 million Medicare beneficiaries have prescription drug coverage, either through the new program or through their employer or other public programs. About 3 million prescriptions are filled a day under the drug benefit program.