To explore user perspectives on applying the Grading of Recommendations Assessment, Development and Evaluation (GRADE) to systematic reviews of complex interventions.Thirty-three authors of recent (2013 onward) systematic reviews were contacted regarding their perspectives on using GRADE from three Cochrane review groups: Cochrane Developmental, Psychosocial, and Learning Problems Group; Cochrane Public Health Group; and Cochrane Depression, Anxiety, and Neurosis Group. Framework Analysis was applied to the data to identify the challenges in applying GRADE and suggestions for its extension, that is, adaptation. These two themes were cross-compared between the groups of answers from "simple" vs. "complex" intervention review authors to identify the specific perspectives on using GRADE in reviews of complex interventions.Specific challenges were identified in applying GRADE to reviews of complex interventions. These were related to the assessment of nonrandomized studies and performance bias in GRADE. Authors perceived these challenges to contribute to frequent downgrading of the "best evidence possible" for complex interventions. Meanwhile, GRADE was found to lack an analytic approach to enable adequate evidence synthesis and assessment of intervention implementation elements.Users suggest that the GRADE guidance be extended to address-specific considerations for complex interventions.