MASSACHUSETTS CONSUMERS may be spending too much for popular generic prescription drugs if they use their insurance instead of paying with cash, according to research released on Wednesday by the Health Policy Commission.

The commission analyzed 1.15 million insurance claims for 10 generic prescription drugs and found that the difference between using insurance (copays, co-insurance, or deductibles) as opposed to tapping the best available cash offer was $1.9 million.

“This is a pretty shocking issue,” said Stuart Altman, the chair of the commission.

Members of the Health Policy Commission struggled with how best to use the information. Altman said signage at pharmacy counters might be used to alert consumers to price differentials while others wondered whether pharmacists themselves should be charged with steering customers to the lowest-priced product.

Nationally, some of the companies that handle prescriptions for health insurance plans have been accused of barring pharmacists from notifying customers if they could pay less using cash. But the commission said a survey of 13 health insurance companies in Massachusetts found the pharmacy middlemen did not have gag rules in place.

In the commission study, officials analyzed insurance claims to find what consumers paid for 10 popular generics in 2015 and compared that cost to what they would have paid using cash in late September using GoodRx, an online drug discount shopping website. The officials said the three-year time difference was considered acceptable because they assumed the best cash price would have been relatively stable over the past few years.

“The difference in years also makes the results more conservative, since if there were systematic changes in cash prices, we would expect that cash prices were lower in 2015, which would result in larger overpayment figures,” the commission said in a statement.

For the cholesterol drug simvastatin, the commission found the best cash price was $4 for 30, 20-milligram tablets at Walmart. Other cash prices ranged from $5.26 at Stop and Shop to $10 at Walgreens.

The 2015 claims data indicated consumers paid an average of $7.60 for the pills, a difference of $3.60 from the lowest cash price. A breakdown of the claims data indicated 30 percent of the customers did not pay more than $4, while 38 percent paid up to $5 more, 25 percent paid between $5 and $10 more, and 6.3 percent paid more than $10 more.

Adding up the overpayments on all 10 drugs, the total came to $1.9 million. Officials said the analysis focused on a relatively small sampling of drug claims. They also said overpayments may be less common but dollar amounts might be greater with some branded or more expensive generic drugs.