Green Light Therapy for Pain and Pain-Related Psychosocial Outcomes: A Systematic Review of Human Studies

Background/Objectives: Pain and psychosocial distress are highly prevalent across acute and chronic medical conditions and may negatively affect quality of life, treatment adherence, and clinical outcomes. Green light therapy has emerged as a non-pharmacological intervention that may modulate neural, inflammatory, and sensory pathways involved in nociception and affective processing. This systematic review evaluated the current human evidence on green light therapy for pain, with consideration of pain-related psychosocial outcomes. Methods: A systematic search was conducted in PubMed, Scopus, Embase, Cumulative Index to Nursing and Allied Health Literature (CINAHL), and PsycINFO for English-language human interventional studies of green light therapy reporting pain. Records were screened in Covidence by independent reviewers using predefined eligibility criteria. Risk of bias was assessed using the Cochrane Risk of Bias 2 (RoB 2) tool for randomized studies and Risk Of Bias In Non-randomized Studies of Interventions (ROBINS-I) for non-randomized studies. Certainty of evidence was evaluated using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) framework. Results: Of 2040 citations identified, 13 studies met inclusion criteria (9 randomized controlled trials, 4 non-randomized studies; 668 participants). Clinical populations included migraine, dental anxiety, fibromyalgia, autism spectrum disorder, and retinal examination discomfort. Most studies reported findings favoring green light, providing an encouraging evidence base that would be strengthened by future blinded, controlled designs. Certainty of evidence was very low for all outcomes across both comparisons. Conclusions: Preliminary evidence suggests green light therapy is a promising and accessible nonpharmacological approach for pain or pain-related psychosocial outcomes but remains insufficient to establish the efficacy of green light therapy. Well-designed, adequately powered, pre-registered, sham-controlled trials with blinded outcome assessment represent a clear and achievable path toward establishing its clinical role.