Melatonin for Neuropathic Pain: Protocol for a Double-blind, Randomized Controlled Trial

Background: Neuropathic pain (NP), a complication of several conditions (eg, diabetic neuropathy and varicella zoster), is a common challenging problem, and there is a growing need to develop safe and effective nonopioid treatments. Sleep disturbance is commonly associated with NP because pain intensity in NP conditions is often worse at night. The pineal hormone melatonin has been shown to reduce pain in both preclinical and clinical settings, in addition to multiple trials demonstrating efficacy for primary insomnia and delayed sleep phase syndrome. Objective: We propose to conduct a clinical trial to evaluate the efficacy and safety of melatonin for NP. Methods: Using a double-blind, placebo-controlled, crossover design, 30 adults with NP will be randomly allocated to one of two sequences of treatment with melatonin and placebo. During each of the two treatment periods, participants will take capsules containing melatonin or placebo for 4 weeks, followed by a 7-day washout period. The primary outcome will be mean daily pain intensity (scored 0-10) at maximally tolerated doses (MTDs) during each period. Secondary outcomes, assessed at MTDs, will include global improvement, adverse events, mood, and quality of life. Results: This trial was registered in the International Standard Randomized Controlled Trial registry May 4, 2022 (ISRCTN #16215617), attained conditional ethics approval May 9, 2022 (Queen's University Health Sciences & Affiliated Teaching Hospitals Research Ethics Board protocol number ANAE-387-22), and recruitment is set to start August 2022. Conclusions: This trial will provide rigorous evidence comparing the efficacy of melatonin to that of placebo in the treatment of NP. Trial Registration: ISRCTN Registry 16215617; https://www.isrctn.com/ISRCTN16215617