A surprisingly large number of people with diabetes are using less insulin than prescribed because of the rising cost of the drug, putting themselves in danger of serious complications. Those are the findings of a small new study by researchers at Yale University, who found that at one clinic in New Haven, Conn., one in four patients admitted to cutting back on insulin use because of cost.

Everyone with Type 1 diabetes needs to take insulin, while about a third of those with Type 2 diabetes do. Not getting enough insulin can have severe consequences for someone with diabetes who does not produce enough of the hormone, which regulates levels of glucose in the blood. Within a week or so without insulin, people with Type 1 diabetes die.

Between 2002 and 2013, the price of insulin jumped, with the typical cost for patients increasing from about $40 a vial to $130 . The amount of insulin a person needs varies, but one vial typically lasts about a week or two.

The Yale team launched the recent study to assess how many people are affected by the rising prices. They surveyed 199 patients in the New Haven area who had either Type 1 or Type 2 diabetes, asking them six questions about their ability to afford insulin, including “Did you use less insulin than prescribed because of cost?” and “Did you not fill an insulin prescription because of cost?” A positive response to any of the six questions counted as insulin underuse.