BackgroundTo explore the feasibility, safety and potential benefits from administration of nandrolone to patients in the recovery phase from critical illness weakness.MethodsIn this phase 2 randomized controlled trial, adult critically ill patients admitted for longer than 7 days with significant weakness, received nandrolone ((males 200 mg, females 100 mg) or placebo weekly, up to a total of three doses. Primary outcome measures were improvement in grip strength, medical research council (MRC) muscle strength sum score, and functional activity level (Chelsea critical care assessment tool (CPAx)).Results22 patients were enrolled between September 2017 and May 2019. No significant adverse events were detected. Median grip strength change was non-significantly greater in the nandrolone group (left hand (9.9 vs 4.4, p = 0.190), right (5.8 vs 3.0, p = 0.343)). The discharge CPAx and ICU mobility scores scores were higher in the nandrolone group, although there was no difference in the change in CPAx score (16.4 vs 17.2, p = 0.865). There were no changes in ultrasound detected muscle thickness between groups.ConclusionsIn patients with prolonged critical illness, nandrolone appears to be safe but a larger study, potentially combined with resistance exercise, is needed to definitively address the potential benefits.Trial registration: ANZCTR registration number : ACTRN12616000835448. Registered 27/6/2016.https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=370920