Researchers say many people still think they are using unadulterated cocaine or crack — a misconception that can be deadly. “Folks who are using stimulants, and not intentionally using opioids, are unprepared to respond to an opioid overdose,” said Brown University epidemiologist Jaclyn White Hughto, “because they don’t perceive themselves to be at risk.” Hughto is a principal investigator in a new, unpublished study called “Preventing Overdoses Involving Stimulants.”