(CNN) The retail price of prescription drugs commonly used by older Americans has continued to increased faster than inflation, according to a new analysis from AARP. This marks the 12th year in a row that there has been a substantial increase in prices.

AARP's Public Policy Institute looked at the retail prices of 754 widely used brand name, generic and specialty drugs used by older Americans and found that the cost increased by an average of 4.2% in 2017 -- twice the rate of general inflation for that same time period. This is lower than the drug price increases observed in previous years, but it's a tepid improvement.

For example, a drug used regularly with a retail price of $19,816 for 2017 would have cost only $7,263 if the price increase was in line with general inflation from 2006 to 2017, the report found.

"If you take a look at what people are bringing in a year with social security on average, that's almost 20% higher," said Leigh Purvis , director of health services research at AARP's Public Policy Institute. "It's also approaching the median income for Medicare beneficiaries. That means these drugs are not affordable if they exceed a person's average year income.

There is no one drug that is driving the trend of higher prices, although there are drugs that have been in the news for their "eye-popping prices," including insulin and some cancer drugs, Purvis said, and there "is no sign of slowing" in this trend.