Tongkat ali is the root of Eurycoma longifolia, a slender shrub that grows in the rainforests of Malaysia, Indonesia, Thailand and Vietnam. The name means Ali's walking stick in Malay, a nod to the long, twisted roots. It is also known as Malaysian ginseng or pasak bumi, and it has an intensely bitter taste.
In South-East Asian tradition the root is boiled and drunk as a tonic, and tongkat ali is traditionally used to support male vitality and energy. In supplements it usually appears as a standardised water extract of the root, often freeze-dried, and the label may state the content of eurycomanone, one of its key compounds and a useful guide to an extract's strength.
Researchers have studied tongkat ali in a number of trials in men. A 2022 meta-analysis of five small randomised trials found higher total testosterone levels in men taking it, especially those with low levels to begin with, while some other trials found no effect. The studies were small and varied in design, so larger trials are needed before firm conclusions can be drawn.