Most people who misuse opioids are first exposed to the drugs through prescriptions so improving prescribing is targeted as one way to help curb the nation’s opioid abuse epidemic. A new study identified six types of risky opioid prescriptions and found that all were linked to a higher chance of death, including fatal opioid overdoses. The study found more than 6 percent of Massachusetts adults received a risky opioid prescription during a five-year period.