Effect of Eurycoma longifolia Jack (Tongkat ali) extract on human spermatozoa in vitro

Eurycoma longifolia (Tongkat ali; TA) is a Malaysian shrub used to treat various illnesses including male infertility. Considering that TA is used to improve male fertility and no report regarding its safety has been published, this study investigated the effects of TA extract on various sperm functions. Semen samples of 27 patients and 13 donors were divided into two groups, washed and swim‐up spermatozoa, and incubated with different concentrations of TA (1, 10, 20, 100, 2000 μg ml^?1) for 1 h at 37 °C. A sample without addition of TA served as control. For washed spermatozoa, significant dose‐dependent trends were found for vitality, total motility, acrosome reaction and reactive oxygen species‐positive spermatozoa. However, these trends were only significant if the highest concentrations were included in the calculation. Contrary, the increase in the percentage of acrosome‐reacted spermatozoa with increasing TA concentrations is very significant (P < 0.0001), and a significant difference (P = 0.0069) to the control could even be recorded at 20 μg TA per ml. For swim‐up spermatozoa, no trend could be observed. Results indicate that the TA extract has no deleterious effects on sperm functions at therapeutically used concentrations (<2.5 μg ml^?1). However, at very high concentrations, TA may have harmful effects in vitro.