Jonathan Schaefer, Ph.D., L.P., Assistant Professor of Psychology
The Schaefer Lab
Jonathan Schaefer, Ph.D., L.P. Assistant Professor of Psychology, Vanderbilt University
Does long-term cannabis use cause depression? How does growing up in poverty shape risk of ADHD and addiction? Why does smoking predict greater risk of developing a psychotic illness?
Jonathan Schaefer leads methodologically sophisticated research in developmental psychopathology—how and why mental health problems emerge and change over time. Specifically, the Schaefer Lab focuses on the environmental determinants of mental health: people’s lived experiences, exposures, and the things they consume, and how these influence the brain and behavior. Their goal is to identify modifiable mechanisms so that prevention, policy, and clinical care target what works. Many important exposures—chronic poverty, substance use, victimization, or environmental pollutants—cannot be assigned randomly for ethical and practical reasons. That makes cause-and-effect tricky. Take cannabis and depression. If they’re linked, is it because cannabis leads to depression, because people with depression use cannabis to cope, or because both are shaped by shared background factors (like neighborhood conditions or genetic risk)?
To unravel questions like these, the Schaefer Lab uses natural experiments, especially twin comparisons. They study large samples of twins raised together and look for pairs who differ in an exposure. This divergence allows them to re-estimate associations between exposures and outcomes in our twins in a way that controls for everything that twins have in common, including their home, neighborhood, and school environments, as well as genetic risk (especially in identical twins). Through rigorous twin analyses across multiple cohorts, Schaefer demonstrated that adolescent cannabis use has minimal causal long-term effects on mental health and cognitive ability, though frequent use may reduce educational attainment through academic performance effects. This research, captured in a series of publications using data from a sample of over 3000 twins followed for over 30 years, has informed cannabis legalization policy debates
Recent studies by Schaefer Lab Ph.D students include: (1) Ankita Mohan’s work showing childhood ADHD predicts reduced educational attainment through effects on GPA and academic motivation even controlling for shared familial confounds, (2) Ali Sloan’s work showing twin differences in nicotine use predict increased symptoms of psychosis over short but not long timescales, and (3) Kaiya Brand’s work showing that high socioeconomic status in childhood protects against underage drinking but morphs into a risk factor for problematic alcohol consumption in early adulthood.
The Schaefer Lab’s most recent large-scale project has been initiating the Vanderbilt University Twin Research Center (VUTRC), a twin registry that contains demographic and contact information for a large set of research-interested, young-adult twins born in the state of
Tennessee. Twins from this resource will be invited to participate in a variety of studies run by the Schaefer Lab, including a new undertaking launching in Spring 2026 that aims to understand the effects of substance use on mental health, cognitive ability, and brain structure/function using high-frequency assessments and longitudinal biomarkers. Research in the Schaefer Lab is supported by grants from the National Institute on Drug Abuse (NIDA), and integrates behavioral genetics, clinical assessment, environmental measurement, and neuroimaging. Trainees learn causal inference, longitudinal modeling, and twin methods while contributing to open, policy-relevant science. Twins and families in the region interested in participating in his lab’s research can learn more through their webpage describing the Vanderbilt University Twin Research Center (https://www.theschaeferlab.com/vutrc).