The new study brings together two research areas that normally stay separate: individual decision-making and social influence. ‘Addiction isn’t just something that happens inside a person,’ says lead author Jesse Boot. ‘It also happens between people. Our goal was to build a model that captures both for the first time.’

Bringing individual processes and social forces together

Most addiction models focus on one side of the story. Some describe how the brain’s reward and control systems battle it out. Others look at peer influence, social networks and community-level outbreaks. But in reality addiction involves both – internal urges and external pressures.

The new model shows how two internal forces shape substance use over time: a reward-driven system that pushes people to use, and a control system that tries to limit use.

These two forces can shift depending on someone’s experiences. Repeated use, for example, can gradually increase sensitivity to a substance – a process known as sensitisation. At the same time, social circles can either strengthen control (e.g. supportive friends) or weaken it (e.g. heavy-using peers).

Insect insights

To build their framework, the researchers adapted a mathematical model originally developed to explain sudden outbreaks of spruce budworms in Canadian forests. It turns out that the same kind of “tipping point” behaviour – long stability followed by abrupt shifts – also helps explain important phenomena in addiction.

Using computer simulations, the team found that their model naturally mirrored well-known patterns in substance use and dependence:

• People often remain stable over time as abstainers, moderate users or heavy users – unless something disrupts that balance.
• Heavy use typically develops slowly through gradual biological and social changes.
• Quitting or relapsing often happens suddenly, even after long periods of stability.
• Substance use can spread rapidly through social networks, resembling an epidemic.
• Once a community shifts into high use, reversing the trend becomes difficult.
• Leaving a harmful peer group can spark recovery – although some people relapse quickly or after a delay.

‘These are patterns clinicians see every day, but until now, they weren’t captured in a single model,’ says addiction expert and co-author Reinout Wiers. ‘That’s what makes this framework so exciting.’

New predictions for modern addiction challenges

The researchers also extended the model to explore interactions between different substances. For example, they show how vaping and smoking can either compete – with vaping sometimes helping people quit cigarettes – or reinforce each other, depending on the situation.

They also found that increasing the availability of a substance doesn’t always cause more use. Problems arise when availability increases and people’s sense of control weakens – a scenario that echoes the rise of online gambling and opioid crises.

Better prevention, better treatment

By showing how internal psychology and social networks interact, the new model could help policymakers design more effective prevention strategies and also help clinicians understand why recovery often requires social change as well as individual effort.

‘Addiction isn’t just an individual problem or a social problem,’ says principal investigator Han van der Maas. ‘It’s both. And when we model it that way, the pieces finally start to fit.’