"Approximately 12.3% of the respondents -- high school seniors in the United States -- reported lifetime nonmedical use of prescription opioids and 8.0% reported past-year nonmedical use. Table 1 shows the prevalence of motives for nonmedical use of prescription opioids among high school seniors in the United States. The leading motives included 'to relax or relieve tension' (56.4%), 'to feel good or get high' (53.5%), 'to experiment-see what it's like' (52.4%), 'to relieve physical pain' (44.8%), and 'to have a good time with friends' (29.5%).

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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