Virtual Opioid User: Simulating the Effects of Counterfeit Pill Prevalence with a Control Theory Model
Adulteration of illicit opioids with substances such as fentanyl contributes to opioid overdose. In the United States, counterfeit pharmaceutical opioids are common and often adulterated. It is unknown how changes in counterfeit pill prevalence could interact with other variables to affect overdose rates.
We developed a model to simulate an individual’s opioid use over 15-minute time steps for two years. We followed the principles of control theory and opponent-process theory, formalizing representations of several processes (habit, effect, craving) as weighted integrals of opioid concentration, which was modeled pharmacokinetic equation. We simulated a range of counterfeit pill prevalence scenarios (6.5% to 45.5%) centered on baseline 26% prevalence. For each scenario, we simulated dose variability in counterfeit pills and the likelihood of fentanyl adulteration. Finally, we developed a web application (bit.ly/virtual-opioid-user) allowing users to explore the model.
Relative to the baseline of 26% counterfeit pill prevalence, the 39% prevalence scenario had 1.61% more overdoses and the 13% prevalence scenario had 4.02% fewer overdoses. Dose variability mediated the effect of counterfeit pill prevalence. Ceteris paribus, a 10% increase in both counterfeit pill prevalence and dose variability increased the likelihood of fatal overdose by 11%.
Virtual Opioid User (VOU) is a flexible model for microsimulations that require a detailed representation of individual opioid use. In this study, we used VOU to explore the relationship between counterfeit pill prevalence and overdose rates. By adding additional model parameters, VOU could be used to study many other opioid use phenomena.