The researchers examined the use of opioids and found that more than 10 million Americans are taking opioids, with nearly 4 million using it regularly.
The researchers conducted a telephone survey of randomly selected U.S. households including 19,150 subjects aged 18 years or older interviewed from February 1998 through September 2006.
Information was gathered on all prescription and non-prescription medications taken during the preceding seven days. For each recorded medication, information was obtained on reason for use, type of administration, number of days taken in the week before the interview, and total duration of the current use.
The researchers found opioids were used 'regularly' by 2 percent of those surveyed, while additional 2.9 percent used opioids less frequently.
Regular opioid use increased with age, decreased with education level, and was more common in females and in non-Hispanic whites.
The prevalence of regular opioid use increased over time and was highest in the South Central region of the country.
Among regular users, almost half had been taking opioids for two or more years and nearly one-fifth had been taking opioids for five years or longer.