Non-right-handedness is more common across multiple mental health conditions

People with mental or neurodevelopmental disorders are more likely to show non-right-handedness than those without these conditions, according to a second-order meta-analysis published in Psychological Bulletin.

Handedness—the tendency to prefer one hand over the other—is rooted in our biology and brain organization. Most people are right-handed, but left- and mixed-handed individuals comprise a significant minority. Handedness is shaped by both genetic and environmental factors, and emerges early in development, even prenatally. It is also associated with brain lateralization, especially in regions involved in language. Because some mental and neurodevelopmental disorders are also linked to altered brain asymmetry, researchers have suspected that handedness might reflect underlying neurocognitive differences relevant to these conditions.

Julian Packheiser and colleagues examined this possibility more systematically by conducting a second-order meta-analysis: essentially, a meta-analysis of meta-analyses.

The researchers first identified 10 relevant meta-analyses that examined conditions such as ADHD, autism, depression, dyslexia, dyscalculia, intellectual disability, PTSD, pedophilia, stuttering, and schizophrenia. Each meta-analysis included studies comparing individuals diagnosed with a given condition to healthy control groups, and provided data on whether participants were right-handed, left-handed, or mixed-handed.

The research team updated each of these existing meta-analyses by searching for and incorporating newly published studies, adding 33 additional datasets to the original 369, for a total of 402 datasets spanning over 202,000 individuals.

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The final dataset encompassed a broad range of mental and neurodevelopmental disorders, and included detailed information about participant age, sex ratio, handedness classification methods, and geographical location of studies. Data were extracted and reanalyzed using a consistent statistical pipeline. Only studies with both clinical and control groups, clear handedness reporting, and no handedness-based participant selection were included. Key moderator variables were also coded, such as whether the disorder was neurodevelopmental, whether it involved language-related symptoms, and the typical age of onset.

Across all studies, individuals with mental or neurodevelopmental conditions were more likely to show atypical hand preferences, meaning they were either left-handed or mixed-handed, than healthy controls. The overall odds ratio indicated that people with these conditions were about 1.5 times more likely to be non-right-handed.

When looking specifically at left-handedness and mixed-handedness, both were significantly more common in clinical groups, with mixed-handedness showing the strongest association. However, these trends varied substantially depending on the disorder. Schizophrenia, autism spectrum disorder, and intellectual disability showed the most pronounced associations with atypical handedness, while conditions like depression and dyscalculia showed no significant differences compared to controls.

When the researchers explored potential moderating factors, several patterns emerged. Disorders that are classified as neurodevelopmental—such as ADHD, autism, dyslexia, dyscalculia, intellectual disability, and stuttering—showed significantly higher rates of non-right-handedness compared to non-neurodevelopmental disorders.

Additionally, conditions associated with language difficulties were more strongly linked to atypical handedness, supporting the idea that disruptions in brain asymmetry may affect both language and motor function. Among the non-neurodevelopmental conditions, those with an earlier average age of onset, such as schizophrenia and PTSD, also showed elevated rates of non-right-handedness. These patterns suggest that early brain development may play a key role in shaping both handedness and vulnerability to certain psychiatric conditions.

Taken together, the results reveal that handedness differences are not uniformly present across all mental health conditions, but instead appear to cluster in disorders with strong neurodevelopmental components or those that impact language processing and early brain development.

One limitation is that analyses relied solely on categorical measures of hand preference (i.e., right, left, or mixed), due to limited availability of continuous handedness measures. This may have constrained the sensitivity of some analyses.

The research, “Handedness in Mental and Neurodevelopmental Disorders: A Systematic Review and Second-Order Meta-Analysis,” was authored by Julian Packheiser, Jette Borawski, Gesa Berretz, Sarah Alina Merklein, Marietta Papadatou-Pastou, and Sebastian Ocklenburg.