The out-of-pocket cost for the opioid overdose antidote naloxone is too high for many uninsured Americans, according to a new study by the RAND Corporation.

The high cost may be keeping naloxone from saving the lives of more people who overdose on opioids, the researchers said. The study found the average out-of-pocket cost of naloxone for uninsured patients rose by 500% from 2014 to 2018. For those with insurance, the cost decreased 26% during that time, The Hill reports.

Among those without insurance, the average out-of-pocket cost rose from $35 in 2014 to $250 in 2018, the study found. About one-fifth of Americans with opioid use disorder are uninsured, the article notes.

“The price of naloxone is almost certainly an impediment to more-widespread adoption among the uninsured,” study lead author Evan Peet said in a news release. “Policymakers who want to further expand access to naloxone—particularly among the uninsured and vulnerable—need to pay greater attention to the out-of-pocket costs.”