Eurycoma longifolia also commonly known as “Tongkat Ali” is a popular traditional herbal medicine native to Indonesia, Malaysia, Vietnam and also Cambodia, Myanmar, Laos and Thailand and a flowering plant of the family Simaroubaceae.
Tongkat Ali is traditionally used for its potent aphrodisiac effects as well as intermittent fever (malaria) in Asia.
Extracts of E.longifolia are used in folk medicine as an adaptogen and tonic herb for increasing strength, energy and vitality, treating sexual dysfunction, infertility, anti-aging, malaria, cancer, diabetes, anxiety, aches, constipation, exercise recovery, fever, leukemia, osteoporosis, stress, syphilis and glandular swelling.
In Malaysia, Tongkat Ali is commonly referred to as “Malaysian Ginseng” due to its purported adaptogenic effects. Adaptogen herbs help to increase the bodies resistance to stress and increase energy without adverse effects.
Modern clinical research has demonstrated that Eurycoma Longifolia exhibits antioxidant, anti-inflammatory, antimalarial, antimicrobial properties and can restore serum levels of testosterone.
Tongkat Ali, Long Jack, Malaysian Ginseng
The plant is reported to be rich in various classes of bioactive compounds such as quassinoids, canthin-6-one alkaloids, β-carboline alkaloids, triterpene tirucallane type, squalene derivatives and biphenyl neolignan, eurycolactone, laurycolactone, and eurycomalactone, and bioactive steroids.
Among these phytoconstituents, quassinoids account for a major portion of the E. longifolia root phytochemicals. 
Evidence-Based Health Benefits
Adaptogen Of Male Sexual Health
A systematic review published in 2017 the literature analyzed and summarized the human clinical trials which revealed the clinical significance and therapeutic feasibility of EL in improving male sexual health.
The systematic review concluded:
All these studies demonstrated considerable effects of EL on male sexual health disorders.
Among them, 7 studies revealed remarkable association between the use of EL and the efficacy in the treatment of male sexual disorders, and remaining 4 studies failed to demonstrate sufficient effects on male sexual health.
In summary, there is convincing evidence for the prominence of EL in improving the male sexual health. 
May Have Clinical Benefit For Erectile Dysfunction
A systematic review and meta-analysis published 2015 set out to determine the efficacy of Tongkat Ali (Eurycoma longifolia) herbal extract on erectile function improvement.
The systematic review and meta-analysis concluded:
Based on current evidence, the herbal extract of Tongkat Ali may have clinical effect on erectile function. However, more efficacy trials are warranted to further support current evidence. 
A review article published in 2016 summarized the ergogenic effect of Tongkat Ali.
This plant is rich in various quassinoids including eurycolactone, eurycomalactone, eurycomanol, eurycomanone, and eurycomaoside all of which has been reported to contribute to its remedial properties including increased muscle strength, endurance in cycling time, and reduced anxiety and stress.
E. longifolia may have sufficient evidence that elicit benefits on endurance performance and physiological responses in high dosage and longer supplementation.
However, this herb has shown to have psychological aid such as antianxiety properties. Hence, further studies could also focus on the herb’s effects on psychological states and determine if these effects are associated with an improvement in exercise performance. 
Natural Testosterone Booster
A narrative review published 2014 in the Journal of Andrologia described Tongkat Ali’s phytoandrogenic and testosterone boosting effects, as a potential natural TRT (Testosterone Replacement Therapy) alternative.
Eurycoma longifolia (Tongkat Ali; TA) is natural alternative to TRT and has been shown to restore serum testosterone levels, thus significantly improving sexual health.
This includes significant positive effects on bone health and physical condition of patients. In addition, a significant antihyperglycaemic effect and cytotoxicity against PCas cells has been shown. Thus far, at therapeutic concentrations, no significant side effects of the treatment were obvious. Therefore, TA might be a safe alternative to TRT. 
A study published in 2012 also in the Journal of Andrologia gave 76 of 320 patients suffering from late-onset hypogonadism (LOH) were given 200 mg of a standardised water-soluble extract of Tongkat ali for 1 month.
While before treatment only 10.5% of the patients did not show any complaint according to the AMS scale and 35.5% had normal testosterone levels, after the completed treatment 71.7% and 90.8% of the patients showed normal values, respectively.
Thus, Tongkat ali extract appears to be useful as a supplement in overcoming the symptoms of LOH and for the management of hypogonadism.