Vejayan, J. et al. 2021. Glycoprotein Isolated from Eurycoma longifolia (Tongkat Ali) is Capable of Boosting Testosterone Levels in Leydig cells: doi.org/10.26538/tjnpr/v5i6.16. Tropical Journal of Natural Product Research (TJNPR). 5, 6 (Jun. 2021), 1078–1082.