Bill Clinton has said Americans are not aware enough of the dangers related to mixing alcohol with opioids.
The former US president said schoolchildren were not being warned of the risks.
Speaking after he delivered a keynote speech at the World Patient Safety Summit in London, Mr Clinton encouraged those part of the movement to continue in their work.
He said: “One friend of mine had a daughter having trouble with her marriage. He was desperate, he called her every day.”
Speaking of America’s opioid crisis, he continued: “It has been a problem for a decade or more in America and nobody tells these kids when they go to school that you can die if you do this.
“You cannot mix these two things.”
Mr Clinton’s keynote speech on Saturday addressed the need to identify the challenges that are killing patients in order to create actionable solutions.
It came the day after Health Secretary Jeremy Hunt’s speech in which he said doctors and nurses were “terrified” that opening up about their mistakes would see them struck off the medical register.
On Saturday Mr Hunt was presented with the movement’s Beau Biden Humanitarian Award for his work on promoting patient safety.