A randomised, double-blind, placebo-controlled, hybrid parallel arm study of low-dose naltrexone as an adjunctive anti-inflammatory treatment for major depressive disorder
Authors: Plank Julia , Glover Stephanie C , Moloney Ben D , Hoeh Nicholas R , Sundram Frederick , Sumner Rachael L , Muthukumaraswamy Suresh , Lin Joanne C 
Published: September 2022

Background Major Depressive Disorder (MDD) is a leading cause of disability worldwide. Current treatments are ineffective in approximately one-third of patients, resulting in a large economic burden and reduced quality of life for a significant proportion of the global population. There is considerable evidence that increased inflammation may distinguish a sub-type of MDD, there are no validated diagnostic tools or treatments for neuroinflammation in MDD patients. The current study aims to explore the potential role of low-dose naltrexone (LDN), a drug with purported anti-inflammatory properties in the central nervous system, as an adjunctive treatment in patients with MDD. Methods/Design This double-blind placebo-controlled hybrid parallel arm study enables exploration of peripheral and central inflammatory markers with LDN as an approach to investigate inflammation as a pathophysiological contributor to MDD. Eligible participants with MDD (n = 48) will be stratified into high and low inflammatory groups according to levels of high sensitivity C-reactive protein (hs-CRP), and then randomized to receive LDN or placebo for an initial 12 weeks, followed by a further 12 weeks during which all participants will receive LDN. The primary outcome measure will be the Montgomery-Åsberg Depression Rating Scale (MADRS) administered at baseline, 2 weeks, 4 weeks, 8 weeks, 12 weeks, 14 weeks, 16 weeks, 20 weeks, and 24 weeks, to assess effectiveness of the anti-depressant response. Secondary outcomes include the use of MRI techniques including quantitative magnetization transfer (qMT), echo-planar spectroscopic imaging (EPSI), and diffusion-weighted imaging (DWI) to help to elucidate the neurobiological mechanism of LDN, and the inflammatory mechanisms in action in MDD. Electroencephalography, blood samples, cognitive tasks, and additional questionnaires, will also be used to determine if there is a specific profile of symptoms in individuals with inflammatory MDD. Healthy participants (n = 24) will be recruited for baseline outcome measures only, to enable comparison with patients with MDD. Discussion This trial contributes to the literature on inflammation in MDD, including understanding of the pathophysiology and efficacy of anti-inflammatory treatments. The investigation of inflammatory mechanisms in MDD is an important first step in the development of biomarkers to classify patient sub-groups, increase the accuracy of diagnosis, and tailor the approach to patients in clinical practice. This study may provide evidence of the benefit of LDN for groups in whom conventional anti-depressants are ineffective and lead the way for translation into clinical practice. Trial registration The trial was registered in the Australian New Zealand Clinical Trials Registry (registration number ACTRN12622000881730). Registered on 21 June 2022 (https://anzctr.org.au/Trial/Registration/TrialReview.aspx?id=383741&isReview=true).