• Jamie T Carreno-Davidson, Colleen M Castellani, Joseph J Carreno, Jesse P DeLuca, Daniel J Selig, Chau V Vuong, Stefan M Pasiakos, and Bradley M Ritland.
• Military Performance Division, US Army Research Institute of Environmental Medicine, Natick, MA 01760, USA.
• Mil Med. 2024 Feb 27; 189 (3-4): e515e521e515-e521.

IntroductionConsidering the potential of weaponized opioids, evaluating how prophylactic countermeasures affect military-relevant performance is necessary. Naltrexone is a commercially available Food and Drug Administration-approved medication that blocks the effects of opioids with minimal side effects. However, the effects of naltrexone on the health and performance of non-substance abusing military personnel are not well described in the existing literature.MethodsActive duty U.S. Army Soldiers (n = 16, mean ± SD, age: 23.1 ± 5.3 y) completed a series of physical, cognitive, and marksmanship tasks during a 4-day pretrial, a 7-day active trial, and a 4-day post-trial phase. During the active trial, participants were administered 50 mg of oral naltrexone daily. Physiological and biological processes were monitored with a daily review of systems, sleep monitoring, biochemistry, and hematology blood panels.ResultsNaltrexone did not negatively affect physical performance, cognitive functioning, marksmanship, or sleep duration (P > 0.05). Improvements were observed during the active trial compared to the pretrial phase in cognitive tasks measuring logical relations (P = 0.05), matching to sample (P = 0.04), math speed (P < 0.01), math percent correct (P = 0.04), and spatial processing (P < 0.01). Results from biochemistry and hematology blood panels remained within clinically normative ranges throughout all phases of the study. No participants were medically withdrawn; however, one participant voluntarily withdrew due to nausea and reduced appetite.ConclusionsTemporary (7-day) daily use of naltrexone was safe and did not negatively affect physical performance, cognitive functioning, marksmanship ability, or sleep in a healthy cohort of U.S. Army Soldiers.Published by Oxford University Press on behalf of the Association of Military Surgeons of the United States 2023. This work is written by (a) US Government employee(s) and is in the public domain in the US.

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