Loneliness is associated with a wide range of mental and physical health issues across all groups in society. The condition has been subject to previous research, though few treatments have been designed and tested. The purpose of this study was to analyze the effects of internet-based cognitive behavioral therapy (ICBT) and internet-based interpersonal psychotherapy (IIPT) with a randomized controlled design. Potential effects on quality of life and comorbid symptoms were also analyzed. Eventual differences in effect between the treatments were analyzed with an exploratory purpose.

The 116 participants were randomized to ICBT (n = 46), IIPT (n = 46) or a control group (n = 24) where participants were put on a waitlist. Loneliness, quality of life and comorbid symptoms were measured in all groups before and after a nine-week treatment period. At post-measure, the ICBT-group reported significantly lower loneliness (Hedges g = 0.93) and significantly higher quality of life (Hedges g = 0.73) than the control group. No significant differences were found between the IIPT-group and the control group or between the ICBT-group and the IIPT-group. Future research should replicate this study with a larger sample to detect any smaller treatment effects. The results of the SOLUS-study show great potential for ICBT as a treatment for loneliness and calls for further research on the effects of IIPT against loneliness.