At least 28 million Americans have experienced a spike in the cost of their prescription medications in the past 12 months. And for 4 million of them, the price was so high they walked away without their prescription altogether, according to a new Consumer Reports survey.

“We are nearing a crisis point with what Americans can afford for medication, and it's scary," concluded Consumer Reports. "And honestly, as far as we can tell, there are no brakes on it right now. Congress may have a few things up its sleeve, but we're still waiting,”

It was the one topic that both presidential candidates could agree on during the campaign trail last year -- prescription drug prices have become too high.

The reasons behind the spike in drug prices is complicated, but experts point to basic market economics.

“There's nothing that puts a stop to it," said Lisa Gill of Consumer Reports. "Companies can charge whatever they want.”

There are several parties involved that contribute to the rising cost of prescription medications: The drug company that manufactures the drug, and the insurance company that pays for you to have the drug.

What you may not know is there's a middle man -- called a pharmacy benefit manager, or PBM. That's who negotiates prices with the drug companies and the pharmacies, on behalf of the insurance companies.

“It's truly an all backdoor negotiation, it's not anything you or I get to see, but that happens with pharmacy benefit managers,” Gill told NBC News.

Here's how it works. Drug companies set the list prices for drugs, but they set them high. They know no one is actually going to pay that price. Consider it like buying a car: You don't pay the sticker price, you barter with the salesperson and make your best offer. When it comes to drugs, the drug maker, the insurance companies and the pharmacies all barter with the PBM. And the PBM decides who pays what, based on the best offer.

That's why one drug for high cholesterol may be covered at 80 percent, while another drug that does the exact same thing is only covered at 20 percent. Or, why the very same drug at one pharmacy chain costs twice as much as it does at another pharmacy chain. In both cases -- it all depends on what deal the PBM has made.

“So consumers are actually in the center of a battle between insurance companies and drug companies, and the way that they do business.” Gill explains.

Everyone blames the other for high prices. The drug companies blame the PBMs, saying they force them to drive prices up because of all those deals. The PBMs blame the drug companies, saying they wouldn't have to make deals if the prices were lower. And, the insurance companies blame both, saying for whatever reason, prices are just too high.

So, is there any way to solve the problem?

Gill has one solution: “For the actual retail price of a drug to go down, it would take either government intervention or for the marketplace to actually lower the price.”