Purpose <p>Leucine is an essential branched-chain amino acid required for skeletal muscle protein synthesis as a substrate and as a key anabolic signaling molecule primarily via activation of the mTORC1. Leucine supplementation has been proposed to enhance muscle adaptations, with some studies showing improvements in muscle growth. However, results from randomized controlled trials (RCTs) have been inconclusive, potentially due to variations in resistance exercise protocols and Leu dose or duration of supplementation. This systematic review explores the effects of leucine supplementation on resistance-training-induced muscle growth, strength, and recovery in healthy individuals.</p> Methods <p>A systematic literature search was conducted across multiple databases (MedLine, EMBASE, PubMed, Science Direct, Scopus, and Cochrane) to identify RCTs investigating the effect of leucine intake on markers of muscle growth, strength, and recovery in trained adults aged 18 to 40&#xa0;years old.</p> Results <p>A total of 14 RCTs were identified including acute (<i>n</i> = 5) and chronic leucine (<i>n</i> = 9) supplementation. A total of 13 studies did not find significant differences in muscle mass, strength, or recovery between leucine-supplemented and placebo groups.</p> Conclusions <p>The evidence from this systematic review suggests that leucine supplementation does not confer significant benefits in muscle growth, strength, or recovery in healthy, trained young adults.</p>