"The lifetime medical use of prescription opioids was reported by approximately 14.0% of those who did not engage in past-year nonmedical use of prescription opioids, 76.1% of nonmedical users of prescription opioids motivated only by pain relief, 71.4% of those motivated by pain relief and other motives, and 46.7% of those who reported non-pain relief motives only (p < 0.001). Among past-year nonmedical users of prescription opioids, approximately 56.5% of those motivated only by pain relief as compared to 23.1% of those who reported pain relief and other motives, and 14.2% of those who reported only non-pain relief motives had initiated medical use of prescription opioids before nonmedical use of prescription opioids. In contrast, approximately 19.6% of those motivated only by pain relief as compared to 48.3% of those who reported pain relief and other motives, and 32.5% of those who reported only non-pain relief motives initiated nonmedical use of prescription opioids before medical use of prescription opioids."

Source

Sean Esteban McCabe, Phd, et al., "Motives for Nonmedical Use of Prescription Opioids among High School Seniors in the United States: Self-Treatment and Beyond," Archives of Pediatric and Adolescent Medicine, 2009 August; 163(8): 739-744. doi:10.1001/archpediatrics.2009.120.
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