Tongkat ali (Eurycoma longifolia) is traditionally used in Southeast Asian medicine as a remedy for male sexual health and fertility. Modern research has begun to validate some of these traditional claims, though the evidence is still emerging and not yet conclusive. Several small-scale clinical studies and animal experiments have investigated the effects of tongkat ali on male reproductive parameters, including testosterone levels, sperm quality, libido, and erectile function.

Some human studies indicate that supplementation may increase serum testosterone, especially in men with low baseline levels or in those experiencing stress-related reductions in testosterone. There is also evidence suggesting improvements in sperm motility, concentration, and semen volume in subfertile men after tongkat ali supplementation. Additionally, pilot studies and user reports suggest improvements in libido and sexual well-being.

However, the research is limited by small sample sizes, short durations, and methodological variability. Most studies are preliminary and larger, well-controlled trials are needed to provide definitive conclusions. Safety profiles appear favorable in the short term, but long-term effects are not well-characterized. Overall, tongkat ali is justified as a supplement to support the male reproductive system by both tradition and emerging, though not definitive, scientific evidence.