This is the first study to our knowledge that compares patterns of prescription and illicit drug misuse in two large urban areas among diverse samples of young adults who are current misusers of prescription drugs. Lifetime misuse of particular prescription drugs and recent use of illicit drugs closely tracked drug seizure data and largely confirmed our first hypotheses: more frequent misuse of oxycodone, heroin, and cocaine in NY, and more frequent use of marijuana and methamphetamine in LA.¹⁶ Hydrocodone was more frequently misused than oxycodone in LA, which is also consistent with monitoring data.¹⁶ These findings suggest that prescription drugs commonly seized in NY and LA are in fact those most commonly misused in each city, and that variability in local markets of diverted drugs may impact frequency of misuse.

Moreover, variations in local drug markets may be factors in explaining differences in modes of administrating opioids and heroin in each city. For instance, Mexican heroin found in LA is frequently in tar form, whereas Colombian heroin found in NY is commonly in powder form.²⁴ In NY, where sniffing powder heroin is common,²⁵ NY participants more frequently sniffed opioids than LA participants. In LA, where smoking tar heroin is common,²⁶ LA participants more frequently smoked opioids than NY participants. These results suggest that participants may have transferred local practices for administering different forms of heroin in each site, i.e., sniffing and smoking, towards administering prescription opioids. These findings provide support for our second hypothesis which proposed an interrelationship between opioid and heroin use.

Furthermore, our results suggest the differences in heroin markets – both supply and form – did not impact lifetime frequency of injecting prescription opioids. NY participants reported more frequent lifetime heroin use, 90-day use, and heroin injection than LA. However, no differences were found in lifetime history of injecting opioids - about one-quarter of participants in both sites had injected opioids. In other words, greater use of heroin in NY- including injection - did not translate into more frequent injection of prescription opioids in NY compared to LA.

While 90-day opioid misuse did not vary between sites, lifetime data suggest greater misuse and availability of more potent opioids in NY, such as oxycondone, fentanyl, and buprenorphine, than in LA. Significantly, the use of more potent prescription opioids in NY coincided with a more robust heroin market in NY. Previous research indicated that potent opioids were particularly useful towards self-medicating for heroin withdrawal as well as functioning as a substitute when heroin was unavailable.⁵ While prior studies report opioid misuse in cities where heroin is scarce,^27,28 these results indicate active misuse of opioids in cities where heroin is frequently available.²⁹ The fact that young adults accessed both opioids and heroin, for instance, suggests the potential for overlapping markets for prescription and illicit drugs, which is in contrast to the conventional view of separate markets.³⁰

Findings on drug substitution, drug combinations, and polydrug use indicate that prescription drugs in both NY and LA were frequently consumed as a part of a broader repertoire of misuse involving prescription drugs and illicit drugs.^11,14

Opioids and tranquilizers were used as substitutes for other drugs when these drugs were not available. The most common drug combinations reported in the past 90 days were opioids and tranquilizers, cocaine and tranquilizers, and heroin and opioids. Qualitative research among young IDUs suggests that particular drug combinations, such as opioids and tranquilizers, are frequently used simultaneously or consecutively during polydrug using events.⁵ Significantly, the misuse of prescription drugs in polydrug combinations presents a greater chance for both fatal and non-fatal overdose.^31,32

Lifetime history of receiving a prescription for an opioid, tranquilizer, or stimulant was high (88%), particularly for opioids (73%).³³ In both sites, participants were prescribed stimulants at significantly earlier ages than the age of first misuse, suggesting that participants used these drugs as prescribed for an extended period before misusing.³⁴ In contrast, initiation into misuse of opioids and receiving a prescription for an opioid occurred at approximately the same age in both sites. In these cases, several factors may have played a role in initiation, including developing a physical dependence on the prescribed drug, enjoying the novel psychoactive features of the prescribed drug, or inadequate management of pain.^5,35,36 Overall, initiation of prescription drugs occurred during the early to mid-teens, after marijuana and before other illicit substances. In particular, initiation of opioids occurred before heroin and initiation of prescription stimulants happened prior to illicit stimulants. These findings on ages of initiation, in combination with the high percentage of participants who used heroin, cocaine, and methamphetamine, suggest that prescription drugs may serve as pathways to illicit drugs in some cases.^5,37,38

Overall, these results suggest that metropolitan drug seizure data¹⁶ may be accurate predictors of the most frequently misused prescription and illicit drugs among certain subgroups of users in some cities. This information could be useful for the other 20 cities where this data is available in confirming that existing programs are targeting the most commonly misused drugs or developing new types of drug treatment programs for both prescription and illicit drugs. Future studies should conduct longitudinal research on young adults in different cities or regions to examine local drug markets and determine how fluctuations in local drug markets impact patterns of illicit and prescription drug misuse, including use of local drug treatment services. Findings could guide drug treatment providers towards developing programs for future young adult clients who may present increasingly complex histories of drug use.

This study has some limitations. First, results are based upon cross-sectional data. Hence, only associations between variables can be determined rather than causal relationships. Second, the sample is comprised of young adults who were currently homeless and/or had engaged in high-risk behaviors, such as injection drug use or polydrug use, in NY and LA. Consequently, the results may not generalize to the larger population of young adults who are housed or who do not engage in these risk behaviors, or to high-risk young adults in other cities. Nonetheless, the sample represents an important subgroup of young adults who should be included in future studies to better describe the spectrum of prescription drug misuse.

In conclusion, patterns of prescription drug misuse among high-risk young adults in LA and NY appear to conform to and be shaped by differences in local markets for illicit drugs in each city. Our findings indicate that current misuse of prescription drugs in both cities encompasses a broad range of practices, such as sniffing, injecting, polydrug use, and drug substitution, and involves frequent misuse of illicit substances. Initiation into prescription drug misuse was often preceded by being prescribed one or more types of prescription drugs, which was then followed by initiating illicit drugs with similar psychotropic effects. Our results suggest that drug treatment providers may anticipate increasingly complex patterns of prescription and illicit drug use among newly enrolled young adult clients.