The highest prevalence of mental health problems is amongst people aged 18–24, with anxiety disorders and depression the most common disorders in this age group. Few young adults seek and receive effective care, prompting calls for the development of ‘youth friendly’ services. The Internet is a modality that has the potential to facilitate engagement with, and delivery of psychological treatments to, young adults. To date, however, no therapist-guided Internet-delivered treatments have been developed specifically for young adults experiencing depression and anxiety.

To examine the efficacy and acceptability of a new therapist-guided Internet-delivered treatment for young adults aged 18–24 with symptoms of depression and anxiety.

Participants accessed the Mood Mechanic Course, which consisted of four lessons delivered over 5 weeks. Measures of depression, anxiety, distress and disability were gathered before and after treatment, and at 3-month follow-up. Results were provided by 78% and 83% of participants at post-treatment and 3-month follow-up, respectively. Data were analysed using mixed linear model analyses. The trial was registered as: ACTRN12612001099819.

Treatment significantly reduced depression and anxiety symptom severity, disability and distress at post-treatment and 3-month follow-up. Large within-group effect sizes were found at post-treatment and 3-month follow-up on all measures using both completer and estimated marginal means (Cohen’s d = 1.02 to 1.41 and 0.94 to 1.45, respectively). The therapist spent an average of 37 minutes (SD = 18 minutes) in contact with participants during treatment. Participants rated the treatment as acceptable.

Treatment gains recorded at post-treatment were sustained at 3-month follow-up, and were consistent with those reported in meta-analyses of Internet-delivered treatments developed for the broader adult population with depression and anxiety. These results provide encouraging preliminary evidence for the efficacy of therapist-guided Internet-delivered treatments for anxiety and depression tailored for young adults.