People who use drugs regularly may have a harder time consistently acting on the negative effects rather than simply ignoring them, a new study published in 2006 has found. translational psychiatry.
Traditionally, scientists have argued that people with more severe drug use are less susceptible to adverse effects such as health problems and economic losses. However, real-life decisions are rarely that simple. People often face competing costs. For example, withdrawal symptoms and loneliness if you stop using, and long-term harm if you continue using. These decisions are also made in stable or constantly changing environments, adding further complexity.
The researchers behind this study therefore wanted to move beyond simplistic models of decision-making. Rather than focusing solely on rewards or a single type of cost, they investigated how people compare multiple costs and how their decisions change depending on the stability of the environment.
A Yale team led by Sonia G. Lewis recruited 137 adults between the ages of 18 and 65 from the community, 75% of whom had a history of regular drug use. To measure the severity of substance use, researchers calculated each participant’s cumulative lifetime “years of regular use” (defined as using a substance three or more times per week).
Participants then completed a computer-based task designed to mimic real-world decision-making under uncertainty. In each of the 200 rounds, you choose between two choices represented by cards and can lose small amounts of random money ranging from $1 to $5. The goal was to minimize losses by learning which options are safer.
The task included two different conditions. In the “steady” state, the probability of losing money remained the same over time. This means that participants can rely on consistent patterns. In “unstable” conditions, the probabilities change frequently, requiring participants to adapt quickly and pay more attention to recent outcomes. Participants were not told when these changes would occur and were forced to learn through experience.
As expected, most participants learned from the feedback and gradually improved their choices. They were more likely to stick with options because it helped them avoid losses ($0 loss), especially in steady states where patterns were easier to detect. This showed that, overall, people can use past results to guide future decisions.
However, a different pattern emerged among individuals who used drugs regularly for more years. These participants were significantly less likely to repeat a choice that only helped them avoid a loss. In other words, even when they made beneficial decisions, they often failed to stick to them. Instead of adopting a successful strategy, they tend to switch choices, whether they have avoided a loss or incurred a loss, suggesting widespread inconsistency in how they use feedback.
This contradiction was especially pronounced in steady state, where the best strategy was to recognize and stick to safer options. Instead, those with a more extensive history of drug use exhibited more erratic behavior, including switching choices even when the environment did not warrant it.
To better understand why, researchers used an advanced computational model (hierarchical Gaussian filter) to analyze the decision-making process. The analysis revealed that people who had used drugs for longer years were less consistent in using “expected value” (the mathematical balance between probability and magnitude of loss) to guide their choices. Clinically, this suggests that people with a history of heavy drug use are not necessarily unaware of the consequences. Rather, their brains have a hard time consistently applying what they learn about those outcomes to future decisions.
“These results suggest that inconsistency in the use of cost information, rather than cost insensitivity, may influence the choice to continue substance use despite negative consequences, contributing to the conceptualization of substance use severity,” Lewis et al. concluded.
The researchers caution that the study has limitations. For example, this task involves financial losses rather than real-life substance-related decisions (e.g., drug cues) and may not fully capture the emotional and social pressures people face. Furthermore, although this study measured cumulative years of use as an indicator of severity, it did not distinguish between current and past drug users.
The study, “The Relationship Between Regular Substance Use and Cost Comparison in Stable and Unstable Learning Environments,” was authored by Sonia G. Lewis, Samuel Paskewitz, and Ariel Baskin Somers.
