March 23, 2026 – Dopamine and opioids, long cast as the chemistry of pleasure and reward, may not function as feel-good messengers but as physiological agents that optimize the body’s metabolic budget, according to a new study by researchers at the Hebrew University of Jerusalem (HU). 

The research, published in Neuroscience and Biobehavioral Reviews, challenges one of neuroscience’s most enduring ideas: that the brain’s reward system exists to make us feel good. Instead, researchers argue that it is built to optimize energy. Long-held beliefs indicate that dopamine is the “wanting” molecule that drives us toward goals, and opioids are the “liking” molecules that provide the hit of pleasure once we get there. But this pleasure-centric view has a major flaw. It doesn’t explain why these same chemicals are active during stress, pain, or even immune responses.  

In this view, motivation arises from rising physiological needs, and reinforcement is the gain when those needs are resolved, according to the study by Matan Cohen and Prof. Shir Atzil of the Department of Psychology at the Hebrew University. 

The research reframes reward not as a subjective feeling, but as a biologically grounded and quantifiable function, redefining the reward system and the roles of dopamine and opioids as mechanisms that optimize the body’s energy economy. It also carries far-reaching implications for both mental and metabolic disorders, including schizophrenia, depression, addiction, diabetes, and obesity. These conditions may be better understood as disruptions in the brain’s ability to efficiently regulate the body’s energy budget, metabolic dysfunctions that may share common neural mechanisms. By identifying these shared metabolic roots, this framework opens new avenues for treatment, focusing on restoring efficient physiological regulation.

The Brain’s Energy Budget

In this new model, dopamine and opioids are redefined, not as reward agents, but as physiological agents: 

• Dopamine (The Mobilizer): Upregulates physiological processes, increasing arousal and mobilizing resources, preparing the body to meet a challenge. 
• Opioids (The Stabilizer): Downregulate these same processes, returning the body to a stable, energy-saving baseline once the challenge is resolved. 

Professor Atzil  explains, “Reward is a measurable biological mechanism aimed at optimizing energy management. This is a basic evolutionary principle that unites physiological regulation, learning, and behavior.”

From Digestion to Social Bonding
The researchers review extensive evidence that this metabolic dance happens across all bodily systems. While we think of dopamine and opioids in the context of reward, learning, or drug addiction, they are busy regulating digestion, respiration, and the immune system. Even complex human experiences, such as art, music, and social bonding, fit this model. A mother’s bond with her child or the thrill of a romantic encounter isn’t just “emotion,” it’s a sophisticated physiological strategy that the brain has learned helps maximize our physiological gains.

“Instead of viewing dopamine and opioids as signals of pleasure, we propose that they function as components of a physiological regulatory system that optimizes energy expenditure over time, through learning processes that lead to physiological and behavioral adaptations,” says Matan Cohen. 

The research paper titled “A metabolic framework for reward: Redefining dopamine and opioids as physiological agents” is now available in  Neuroscience & Biobehavioral Reviews and can be accessed here.

Researchers: 

Matan Cohen, Shir Atzil 

Institutions: 

Department of Psychology, The Hebrew University of Jerusalem, Jerusalem, Israel