Mental health and addiction: a population-based approach at the Collège de France

Congratulations Maria Melchior, you have just been appointed to the Collège de France's Chair of Public Health on the theme of “Mental health and addiction: from individual suffering to population-based action.” Can you tell us about this chair?
The Chair of Public Health at the Collège de France has been in existence since 2018 and invites a leading figure in the field to hold the chair for one year. It addresses a variety of topics related to public health. In 2025, in the context of the national cause dedicated to mental health, it was decided that the chair should focus on this subject.
My inaugural lecture will take place on December 4. It will be followed by two lectures before the end of the year, then a series of six lectures, every Monday from 10 to 11 a.m. (https://www.college-de-france.fr/fr/chaire/maria-melchior-sante-publique-chaire-annuelle/events). I have invited several colleagues—sociologists, biologists, economists—to share their perspectives. The goal is to approach mental health from a multidisciplinary perspective, in relation to social inequalities and the social determinants of health.
Finally, an international conference is planned for May 29, 2026, which will extend these discussions.

What do you hope to develop through this chair?
I am very honored by this appointment. The Collège de France was founded to teach new knowledge that is not yet widely available in traditional universities.
What is particularly important to me is to raise awareness of social epidemiology, an approach that is still rarely taught in France. I want to show how it can be used to analyze social inequalities in mental health and addiction.
The courses will also address how mental disorders are defined through medical classifications such as the DSM or the ICD, as well as the social factors that influence their onset—work, housing, family, living conditions, etc. The idea is to show mental health in all its complexity, between medical sciences and social sciences.

Can you tell us about your career path and what led you to mental health and addiction?
My career path is quite unusual. I started by studying psychology in the United States, with a strong scientific focus: neuroscience, cognitive science, statistics. Then I moved into public health, specifically social epidemiology.
I joined Inserm in 2007, at a time when psychiatric epidemiology was still in its infancy in France. There was some clinical research, but few population-based studies. I wanted to help fill this gap by working on the social determinants of mental disorders and addiction.

So how do we define mental health from an epidemiological perspective?
In epidemiology, we rely on international medical classifications (the DSM and ICD) to identify psychiatric disorders.
We work on surveys of the general population, focusing on the most common disorders: depression, anxiety disorders, ADHD, as well as addiction to tobacco, alcohol, or cannabis.

How do you work on these issues in practice?
We mainly conduct quantitative surveys. These cover both the general population and marginalized groups—homeless people, undocumented immigrants, etc.
We use longitudinal cohorts such as Constances and Elfe, which follow thousands of participants over time, and a cohort that our team has been piloting for a long time, Tempo, which allows us to analyze mental health trajectories from childhood to adulthood.
We also carry out interventional studies to test prevention or support measures aimed at reducing social inequalities.

What do you think are the main social determinants of mental disorders?
Poverty and lack of financial resources are major factors. We see a very clear social gradient: the more unfavorable the living conditions, the more frequent mental disorders are. Added to this are food insecurity, job instability, and precarious housing. These situations generate stress and contribute to ill-being.
It is also important to highlight the decisive role played by violence suffered during childhood and adolescence—whether it be maltreatment, neglect, sexual abuse, or psychological violence—the psychological consequences of which can be profound and long-lasting. These traumatic experiences often interact with unfavorable social conditions, reinforcing inequalities in mental health.
Poverty currently affects around 15% of the French population, and food insecurity affects nearly 10%—figures that continue to rise.

What recommendations would you make to public authorities?
First, healthcare provision needs to be better adapted to actual needs. The most vulnerable people are often those with the least access to psychological or psychiatric care.
There are specialized facilities, but there are not enough of them.
We also need to take action upstream, addressing social determinants such as housing, employment, and economic security. These levers have a direct impact on mental health, even if they go beyond the medical field alone.

When it comes to addiction, have you noticed any new trends?
Yes, non-substance addictions are on the rise. Gambling addiction is nothing new, but online platforms and sports betting have contributed to its growth.
Video game addiction is now recognized as a pathology by the WHO, and there is also discussion about social media addiction, which raises questions about our relationship with screens, pleasure, and self-control. It should be noted, however, that levels of tobacco, alcohol, and cannabis use are declining significantly, particularly among young people, which is an encouraging development in terms of public health.

Is there a causal link between mental health issues and addiction?
The two reinforce each other.
Certain psychological predispositions, such as impulsivity or ADHD, increase the risk of addiction.
But conversely, substance use (alcohol, cannabis) can promote the development of depression or anxiety disorders in the long term.
Fortunately, it's never too late to quit: the health benefits are visible, regardless of when you stop using.

Since the pandemic, mental health has become a national priority. How does the “Grande cause nationale” (Great National Cause) contribute to this?
This initiative follows surveys conducted during the Covid crisis, which showed a marked deterioration in mental health, especially among young people.
It has led to concrete measures such as the “Mon soutien psy” (My psychological support) program, which is now accessible to all and reimbursed, to promote earlier access to psychological care.
This is progress, even if regional inequalities remain: finding a psychologist is easier in Paris than in some rural areas.