One study on the effects of supplementing with Tongkat Ali found:

How to Increase Testosterone Naturally with Tongkat Ali

Longjack 200 : 1 - Tongkat Ali 400mg Premium Extract - Natural Testosterone Booster (1 Bottle 60 Capsules)

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  • Although not everyone who supplements with tongkat ali wants to increase their fertility, it is worth mentioning that tongkat ali’s hormonal support benefits also promots normal sperm quality. Sperm quality, measured by volume, concentration, and motility, can impact male fertility. [9]

    That said, if you’re a middle aged male who is experiencing the symptoms of andropause and feel it’s time to put a spring back into your step, consider supplementing with tongkat ali. The research is positive and do not indicate any negative side effects. If you combine herbal support with a healthy diet and regular exercise, you may have a winning formula.

  • It’s not your fault. Your testosterone has been declining by roughly 1% per year, every year since you were 30. You now have a choice to make. You can either continue down the path of aging and going quietly into the night, or you can be proactive and regain that edge with Tongkat Ali.

    A 2012 study out of Malaysia consisted of seventy-six men, only 35% of whom had normal testosterone levels. After one month of supplementing with tongkat ali, the number of men in the group with normal testosterone levels jumped to over 90%. [7]

  • You can find tongkat ali promoted as 4:1, 5:1, 10 to 1, 20:1, 50:1, 100:1 and 200:1 extract concentrations. These can be misleading since there are no accepted scientific standards as to what a particular concentration of the herb has to be before it is called a 4:1 or a 50 to 1 extract. Thus various promoters claim their product is a 20 to 1, 50 to 1, 100 to 1 or 200 to 1 extract. These claims are not helpful. What are they basing their high potency claim on? There are quite a number of different chemicals and substances within the tongkat ali root. There are no standards that say a 40% glycosaponin content constitutes a particular extract concentration. Therefore there is no such thing as a 50 to 1, 100 to 1, or 200 to 1 extract and any company who claims they are selling a product that is 200 times as potent as the regular powder is misleading the consumer. The only way to find out what is in their product is to do a chemical analysis known as an HPLC test to determine the various ratios and contents of glycosaponins, eurypeptides, quassinoids, and the other active ingredients within the plant.

Tongkat Ali Root Extract – Eurycoma Longifolia - WebMD

Previous studies have shown properly-standardized TA to stimulate release of free testosterone, improve sex drive, reduce fatigue, and improve well-being. We assessed stress hormones and mood state in 63 subjects (32 men and 31 women) screened for moderate stress and supplemented with a standardized hot-water extract of TA root (TA) or Placebo for 4 weeks. Significant improvements were found in the TA group for Tension (-11%), Anger (-12%), and Confusion (-15%). Stress hormone profile (salivary cortisol and testosterone) was significantly improved by TA supplementation, with reduced cortisol exposure and increased testosterone status. Results indicate that daily supplementation with tongkat ali root extract improves stress hormone profile and certain mood state parameters, suggesting that this "ancient" remedy may be an effective approach to shielding the body from the detrimental effects of "modern" chronic stress, which may include general day-to-day stress, as well as the stress of dieting, sleep deprivation, and exercise training.