Combination medications make patients' lives easier — who wants to deal with three different pills when they can just take one? But this convenience often comes at a high cost.

The price of these drug combinations, sometimes called polypills, can be over four times what they would be if the individual medications were purchased separately. That's a lot to pay for convenience.

This can mean that prescriptions for three medications that cost $20 a month could rise to about $90 if the medications were combined and purchased as a polypill. If the prescriptions had originally cost $100 a month, the polypill version would be about $450. That's likely to give anyone sticker shock.

While this study looked at a very specific set of 29 combination medications, not at combination meds in general, these pills' higher costs add up to a lot of money. The people who take them may not care much — if their insurance pays for the meds — but someone is spending a lot of extra money for the convenience of these polypills.

Drug companies like combination medications. By combining drugs they have an opportunity to keep at least part of a drug's market when generic replacements become available.

To find out how much extra money combination meds were costing Medicare, researchers at Harvard University and Brigham and Women's Hospital first looked at the 1,500 drugs that Medicare spent the most money on in 2015. Only 170 of these were combination drugs. They excluded those combination drugs that were generics, not oral medications or could not be replaced by generic drugs. This left the researchers with the 29 combination meds that were likeliest to cost substantially more than their single-dose counterparts.

They estimated that the 29 brand-name pills that could be replaced by generic versions of their individual components cost Medicare an extra $925 million. One of the combination pills the team tracked was the blood pressure drug, Exforge. It is a combination of two drugs, amlodipine and varsatan, and cost $8.21 per pill at the time of the study. Taking the same dose of these two generic components would cost $.96. Exforge's price was over eight times higher.

Not all polypills are so much more expensive than their individual constituents. The study did not look at polypills that were available as generics and reasonably priced. But it does make clear that patients and doctors might want to check price before choosing a combination drug.

The cost of prescription drugs is one of the biggest reasons that healthcare in the United States is so expensive. And these combination medications are striking examples of ballooning drug costs that can be easily avoided.

Drug companies like combination medications because they offer an opportunity to keep at least part of a drug's market when generic replacements become available. Companies often begin selling a combination medication shortly before the generic version of their ingredients become available, strongly suggesting that polypills may be even more convenient for the pharmaceutical companies than for the people who take them.

The study appears in JAMA.