Eurycomanone is a major quassinoid compound found in Eurycoma longifolia, commonly known as tongkat ali or longjack. While tongkat ali has a long history of traditional use as a general tonic and libido enhancer in Southeast Asia, its application for bodybuilding specifically is supported by emerging but limited scientific evidence, largely due to the potential effects of eurycomanone on testosterone levels. Several in vitro and animal studies suggest that eurycomanone can stimulate the production or release of endogenous testosterone by suppressing aromatase activity and supporting the hypothalamic-pituitary-gonadal axis. Human studies on tongkat ali extracts (standardized for eurycomanone content) have shown modest increases in testosterone levels and improvements in muscle strength and body composition when combined with resistance training. However, these studies are generally small, short-term, and often use whole plant extracts rather than isolated eurycomanone.

There is insufficient direct clinical evidence to confirm that eurycomanone alone significantly enhances muscle growth or athletic performance in healthy adults. The evidence base is limited by small sample sizes, heterogeneity in preparation, and lack of long-term safety data. Therefore, while there is a plausible scientific rationale and some preliminary evidence supporting eurycomanone's use in bodybuilding contexts, the current level of support is considered weak to moderate (rated 2/5).