The different stimulation durations of transcranial direct current stimulation for Parkinson’s disease: a systematic review and network meta-analysis

Background Transcranial direct current stimulation (tDCS) holds promise for the treatment of motor symptoms in Parkinson’s disease (PD). However, the optimal stimulation duration within a single session remains unclear. Objective This network meta-analysis (NMA) aimed to compare the relative effects of different single-session tDCS durations (13–30 min, 2 mA) on motor symptoms in patients with Parkinson’s disease. Methods We systematically searched PubMed, Embase, Cochrane Library, and Web of Science up to May 7, 2026 for randomized controlled trials (RCTs) that compared active anodal tDCS at 2 mA with sham stimulation in patients with PD. The primary outcome was the Unified Parkinson’s Disease Rating Scale Part III (UPDRS-III), and the secondary outcome was the Timed Up and Go (TUG) test. Risk of bias was assessed using the ROB 2.0 tool, and the certainty of evidence was evaluated using the GRADE approach. A frequentist network meta-analysis was performed. Results Sixteen RCTs (414 patients) were included. All networks were open-loop. Compared to sham, all active tDCS (2 mA, with durations of 13, 15, 20, 25, and 30 min) showed numerical improvements in UPDRS-III and TUG (0.35–1.03 s), but none reached statistical significance (all p > 0.05). However, probability ranking showed that 2 mA + 15 min tDCS had the highest probability of being optimal for improving UPDRS-III, while 2 mA + 13 min tDCS was most likely to be optimal for reducing TUG time. Owing to sparse indirect evidence, no definitive efficacy ranking can be made, and these rankings are descriptive only. Conclusion No single-session tDCS duration between 13 and 30 min at 2 mA was statistically superior to sham for improving motor function in PD. The current limited evidence suggests that varying stimulation time alone within this range does not decisively impact outcomes. Our findings highlight the need for multidimensional optimization of tDCS and further high-quality RCTs. Systematic review registration https://www.crd.york.ac.uk/PROSPERO/view/CRD42024599000 .