Eurycoma Longifolia Jack is the herb name for what is more commonly known as Tongkat Ali, Malaysian Ginseng, or Longjack.
The aphrodisiac effects of Eurycoma are quite reliable and appear to span a large variety of animal models, limited evidence in female rats but it appears to affect these to a similar extend as in males. It is difficult to do a comparative analysis between other herbal aphrodisiac to assess potency, but Eurycoma is anecdotally one of the better ones.
In addition to the aphrodisiac effects, Eurycoma can also increase sperm production and may directly act as a proerectile agent. At least one molecule in Eurycoma (9-hydroxycanthin-6-one) is associated with both a delay in ejaculation as well as pro-erectile properties (although the ability of this molecule to act via consuming Eurycoma extract is not known).
Hormonally, Eurycoma appears to have remarkable anti-estrogenic effects in vitro and has a potency similar to Tamoxifen when the active ingredient is injected. Promising, but no human studies exist on it currently or studies assessing oral intake of Eurycoma Extract. On the testosterone side of things, the literature appears to be needlessly promising. No peer-reviewed evidence currently establishes Eurycoma as a testosterone booster in otherwise healthy persons or rats but many studies are quick to cite presentations by an M.I Tambi claiming these boosts in testosterone. None of Dr.Tambi's research presented in conferences appears to be indexed in Medline and the claims expressed cannot be proven.