Background

The current study explored whether higher‐ (up to 8 modules) versus lower‐dose (3 or less modules) unguided internet Cognitive Behaviour Therapy for perfectionism (ICBT‐P) was more effective, and the best method to promote higher dosage.

Methods

Two sequential randomised ICBT‐P studies were conducted with participants who self‐identified as having difficulties with perfectionism; in the first participants (N = 51) received 3‐module ICBT‐P or wait‐list, and in the second participants (N = 55) received fixed (asked to complete all 8 modules two per week over 4‐weeks) or flexible format (after completing the first psychoeducational module, participants decided how many/in what order they completed the modules). We examined impact on our primary variables, perfectionistic concerns and standards, and secondary outcomes of negative affect, body image flexibility, and self‐efficacy.

Results

More modules were completed in the higher‐ (M modules = 4.36, SD = 3.29) versus lower‐dose (M = 1.96, SD = 1.23) ICBT‐P, d = 0.86 (95% confidence interval: 0.39, 1.34). The latter impacted perfectionism but not secondary outcomes; the former impacted all outcomes (except for self‐efficacy), and within‐group effect size improvements were double in the high‐ compared to low‐dose ICBT‐P. There was no difference between the fixed and flexible formats in terms of the number of modules completed or impact.

Conclusions

We can offer a patient‐centred approach to ICBT‐P that is effective, while suggesting completion of more modules can result in larger, more pervasive improvements.