A meta-analysis of interventions to reduce loneliness was conducted to evaluate the effectiveness of four primary strategies: improving social skills, enhancing social support, increasing opportunities for social contact, and addressing maladaptive social cognition. The study found that single group pre-post and non-randomized comparison studies yielded larger mean effect sizes compared to randomized studies. Among randomized studies, interventions targeting maladaptive social cognition were most effective, consistent with current theories of loneliness. Theoretical and methodological issues in designing loneliness reduction interventions were discussed. Loneliness is defined as the discrepancy between desired and actual social relationships. It is distinct from social isolation, which is an objective measure of social interactions. Loneliness is more closely associated with the quality than the quantity of relationships. It is a biological construct that serves as a signal to change behavior, similar to hunger or pain. Loneliness can have detrimental effects on cognition and behavior, increasing the likelihood of chronic loneliness. Research indicates a significant prevalence of loneliness among children and adults. Factors such as aging, delayed marriage, and increased single-residence households may contribute to increased loneliness. Loneliness is associated with various health conditions, including increased vascular resistance, elevated blood pressure, and diminished immunity. It is also linked to cognitive decline and progression of Alzheimer's disease. Theories of loneliness suggest it is a fleeting, unpleasant mood for some individuals or a persistent, aversive experience for others. It is approximately 50% heritable and 50% environmental. Loneliness can be exacerbated or ameliorated by social interactions. Previous reviews of loneliness interventions identified strategies such as social skills training, social support, opportunities for social interaction, and cognitive behavioral therapy as potentially effective. However, many studies lacked rigorous design, and the efficacy of interventions remained uncertain. The purpose of the meta-analysis was to quantify the efficacy of primary intervention strategies. The study included 50 studies, categorized by research design. Effect sizes were calculated for each study, with single group pre-post studies and non-randomized group comparison studies yielding larger effect sizes. Randomized group comparison studies showed that interventions targeting maladaptive social cognition were most effective. The study concluded that interventions addressing maladaptive social cognition had a greater impact than those targeting social skills, social support, or opportunities for social interaction. The results highlight the importance of social cognition in loneliness and the need for more rigorous research in this area.A meta-analysis of interventions to reduce loneliness was conducted to evaluate the effectiveness of four primary strategies: improving social skills, enhancing social support, increasing opportunities for social contact, and addressing maladaptive social cognition. The study found that single group pre-post and non-randomized comparison studies yielded larger mean effect sizes compared to randomized studies. Among randomized studies, interventions targeting maladaptive social cognition were most effective, consistent with current theories of loneliness. Theoretical and methodological issues in designing loneliness reduction interventions were discussed. Loneliness is defined as the discrepancy between desired and actual social relationships. It is distinct from social isolation, which is an objective measure of social interactions. Loneliness is more closely associated with the quality than the quantity of relationships. It is a biological construct that serves as a signal to change behavior, similar to hunger or pain. Loneliness can have detrimental effects on cognition and behavior, increasing the likelihood of chronic loneliness. Research indicates a significant prevalence of loneliness among children and adults. Factors such as aging, delayed marriage, and increased single-residence households may contribute to increased loneliness. Loneliness is associated with various health conditions, including increased vascular resistance, elevated blood pressure, and diminished immunity. It is also linked to cognitive decline and progression of Alzheimer's disease. Theories of loneliness suggest it is a fleeting, unpleasant mood for some individuals or a persistent, aversive experience for others. It is approximately 50% heritable and 50% environmental. Loneliness can be exacerbated or ameliorated by social interactions. Previous reviews of loneliness interventions identified strategies such as social skills training, social support, opportunities for social interaction, and cognitive behavioral therapy as potentially effective. However, many studies lacked rigorous design, and the efficacy of interventions remained uncertain. The purpose of the meta-analysis was to quantify the efficacy of primary intervention strategies. The study included 50 studies, categorized by research design. Effect sizes were calculated for each study, with single group pre-post studies and non-randomized group comparison studies yielding larger effect sizes. Randomized group comparison studies showed that interventions targeting maladaptive social cognition were most effective. The study concluded that interventions addressing maladaptive social cognition had a greater impact than those targeting social skills, social support, or opportunities for social interaction. The results highlight the importance of social cognition in loneliness and the need for more rigorous research in this area.