In a study published by JAMA Neurology, researchers found that multiple sclerosis patients who have Medicare Part D—government-funded health insurance that covers prescription drug costs—have seen their medication prices quadruple from 2006 to 2016.

The rise in drug prices has also translated to an increase in patients' out-of-pocket expenses, which increased by seven times over that decade, from $372 a year to $2,673 a year.

Alvaro San-Juan-Rodriguez, an author of the study, told Business Insider that the expenses are "exorbitant" and mean limited drug access for multiple sclerosis patients.

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The high cost of prescription drugs is a growing problem in the US healthcare system.

A new study published by the journal JAMA Neurology sheds new light on the issue, revealing how drug prices for individuals with multiple sclerosis (MS) quadrupled over a 10-year period. The average price of the treatments climbed from $18,660 in 2006 to $75,847 in 2016. That's more than the median family in the US makes each year.

"We were not expecting the magnitude of the drug price increase at all," Alvaro San-Juan-Rodriguez, one of the study's authors, told Business Insider. "The price is exorbitant, and it's higher than what we've seen for other specialty drug medications."

MS is a degenerative inflammatory disease of the central nervous system, which affects almost one million people in the US, according to the National Multiple Sclerosis Society.

The study focused on patients using Medicare Part D, government-funded health insurance that helps cover prescription drug costs. Medicare Part D is available to seniors, as well as to some individuals with disabilities.

The cost of prescription drugs has drawn attention from both Republicans and Democrats, with the Trump administration proposing a number of fixes. Still, the administration has taken little action so far and drug prices continue to increase. Often patients end up paying a significant portion of the cost.

Study authors including San-Juan-Rodriguez and Inmaculada Hernandez at the University of Pittsburgh set out to study the increasing price of multiple sclerosis drugs to see how they affected patients and the healthcare system. They said increasing costs can make it difficult for patients to afford their medications.

MS drug costs have increased exponentially, causing patients to pay more out-of-pocket

The study showed that as the total cost of MS drugs increased, so did the amount that patients had to pay out-of-pocket. Looking at Medicare data, the study breaks down the price increases separately for drug list prices (the cost before any rebates), patients' out-of-pocket expenses, and Medicare expenses.

The study looked at an average of 2.8 million Medicare beneficiaries every year from 2006 - 2016. The annual cost of treatment with self-administered disease modifying therapies (DMTs) for MS patients increased from $18,660 in 2006 to $75,847 in 2016, averaging a 12.8% increase annually, based on the list price of the treatments.

Medicare's actual spending increased by 10 times over that decade, from $7,794 to $79,411 on average. And average out-of-pocket spending increased by seven times from $372 to $2673 over the 10 years.

The chart below from the study shows how the prices of different MS therapies all largely increased at a similar pace.

The graph shows the trends in annual cost of treatment with self-administered DMTs for MS in Medicare Part D. The chart is courtesy of JAMA Network.

Even with new therapies entering the market, drug prices continue to increase

Some of the most popular drugs for MS on the market like Copaxone, Tecfidera and Avonex reduce the frequency of relapses for MS patients.

"These drugs offer great benefits to patients," Rodriguez said. "It helps with vision loss, pain, fatigue and muscle weakness and much more."

Even though there has been increased competition for for MS drugs overtime, as new therapies are introduced, the drug prices have been steadily increasing for almost all the therapies.

"The uptake for the new therapies since they entered the market a couple years ago is considerable," Hernandez told Business Insider. "It's hard to predict the future, but we hope these trends will not be maintained. There should be more competition so we don't see these drug prices continue."

Rodriguez said he hopes this study will be a call to action for drug prices to not continuously inflate.

"We observed how prices of drugs are more than four fold and the key driver is out-of-pocket expenses which reduces patient access for the vital medication they need," Rodriguez said