Tongkat ali is an herbal remedy that has been a part of traditional Southeast Asian medicine for centuries.

It’s often used to treat a variety of ailments, including fevers, erectile dysfunction, and bacterial infections.

Studies suggest that tongkat ali may boost male fertility, relieve stress, and improve body composition, but research in these areas is limited (1, 2, 3).

This article reviews tongkat ali, including its benefits, possible side effects, and dosage.

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Tongkat ali, or longjack, is an herbal supplement that comes from the roots of the green shrub tree Eurycoma longifolia, which is native to Southeast Asia.

It’s used in traditional medicine in Malaysia, Indonesia, Vietnam, and other Asian countries to treat malaria, infections, fevers, male infertility, and erectile dysfunction (4).

The health benefits of tongkat ali likely stem from various compounds found in the plant.

Specifically, tongkat ali contains flavonoids, alkaloids, and other compounds that act as antioxidants. Antioxidants are compounds that fight cellular damage caused by molecules called free radicals. They may benefit your body in other ways as well (3, 5, 6, 7).

Tongkat ali is typically consumed in pills that contain an extract of the herb or as part of herbal drinks (3).

Summary Tongkat ali is an herbal medicine derived from the Southeast Asian Eurycoma longifolia shrub. It contains several potentially beneficial compounds and is used to treat a variety of ailments, including male infertility and infections.

Most of the alleged health benefits of tongkat ali are not well researched, but some studies suggest that it may help treat male infertility, improve mood, and increase muscle mass.

May increase testosterone levels and improve male fertility

Tongkat ali's potential to increase testosterone in men with low levels of this primary sex hormone is well known and well documented.

Low testosterone can result from aging, chemotherapy, radiation treatments, some medications, injury or infection of the testicles, and certain diseases, such as chronic alcoholism and obstructive sleep apnea (8).

Effects of inadequate testosterone levels include low libido, erectile dysfunction, and in some cases, infertility. Since compounds in tongkat ali may boost low testosterone, it could treat these issues (8, 9, 10).

A 1-month study in 76 older men with low testosterone found that taking 200 mg of tongkat ali extract per day significantly increased levels of this hormone to normal values in over 90% of participants (10).

What’s more, studies in both animals and humans show that taking tongkat ali stimulates sexual arousal and may improve erectile dysfunction in men (11, 12, 13, 14).

Finally, tongkat ali may improve sperm motility and concentration, boosting male fertility (1, 14, 15, 16, 17).

One study in 75 male partners of couples with infertility found that taking 200 mg of tongkat ali extract per day significantly improved sperm concentration and motility after 3 months. The treatment helped over 14% of couples become pregnant (1).

Similarly, a 12-week study in 108 men ages 30–55 observed that taking 300 mg of tongkat ali extract daily increased sperm volume and motility by an average of 18% and 44%, respectively (14).

According to these studies, tongkat ali effectively treats low testosterone and infertility in some men, but more extensive research is needed.

May relieve stress

Tongkat ali may lower stress hormones in your body, decrease anxiety, and improve mood.

A 1999 study first identified the possible role of this remedy in treating mood issues and found that tongkat ali extract was comparable to a common anti-anxiety medication in reducing symptoms of anxiety in mice (18).

Similar effects have been seen in humans, but research is limited.

A 1-month study in 63 adults with moderate stress found that supplementing with 200 mg of tongkat ali extract per day reduced levels of the stress hormone cortisol in saliva by 16%, compared to those who received a placebo (2).

Participants also reported significantly less stress, anger, and tension after taking tongkat ali (2).

While these results are promising, more studies in humans are needed.

May improve body composition

Tongkat ali is often claimed to boost athletic performance and increase muscle mass.

This is because it contains compounds called quassinoids, including eurycomaoside, eurycolactone, and eurycomanone, which may help your body use energy more efficiently, reduce fatigue, and improve endurance (3).

In other words, the supplement may act as an ergogenic aid, which is a substance that can enhance physical performance and improve body composition (3, 19).

A small, 5-week study in 14 men participating in a strength training program found that those who took 100 mg of tongkat ali extract per day experienced significantly greater increases in lean body mass than those taking a placebo (20).

They also lost more fat than participants in the placebo group (20).

What’s more, a 5-week study in 25 active older adults discovered that supplementing with 400 mg of tongkat ali extract daily significantly increased muscular strength, compared to a placebo (21).

However, a small study in cyclists observed that consuming a drink with tongkat ali during exercise did not improve performance or strength any more than plain water (22).

These conflicting results suggest that tongkat ali may exhibit some ergogenic effects, depending on the dose and length of treatment, but more research is needed.

Summary Studies show that tongkat ali may boost testosterone levels and help treat infertility in men, relieve stress, and possibly increase muscle mass. Still, more extensive research is needed.

The few studies on the use of tongkat ali in humans have not reported any side effects (1, 2, 21).

One study noted that taking 300 mg of tongkat ali extract daily was as safe as taking a placebo. (14).

Other studies suggest that taking up to 1.2 grams of tongkat ali extract per day is safe for adults, but this amount has not been used in research. Plus, no studies examine its long-term use, making it unclear whether the supplement is safe over longer periods (23, 24).

What’s more, one study examining the mercury content of 100 tongkat ali supplements from Malaysia found that 26% had levels of mercury higher than the recommended limit (25).

Consuming too much mercury can result in mercury poisoning, which is characterized by mood changes, memory problems, and motor skill issues (26).

Furthermore, the effects of tongkat ali in children or pregnant and breastfeeding women have not been researched. Therefore, it’s unknown whether the remedy is safe for these populations.

Summary Tongkat ali appears to be safe in doses of 200–400 mg per day for most healthy adults. However, it’s unknown whether tongkat ali is safe for pregnant or breastfeeding women. Some supplements may also contain mercury.

Some studies suggest that tongkat ali may reduce anxiety and improve body composition, but research is limited.

It may also treat low testosterone, poor libido, and male infertility.

While tongkat ali does not appear to have adverse effects in doses up to 400 mg per day, research is limited, and available studies focus on short-term use.

It’s unclear whether taking the supplements over longer periods is beneficial and safe.

If you’re interested in taking tongkat ali, consult your healthcare provider to ensure proper safety.

Additionally, keep in mind that some supplements may be contaminated with mercury. Plus, they’re not well regulated and may contain more or less tongkat ali than listed on the label. Look for a reputable brand that has been tested by a third party.

Lastly, pregnant and breastfeeding women should not take tongkat ali, due to the lack of research in this area. Additionally, those with medical conditions or taking medications should speak to their healthcare provider before taking tongkat ali.

Summary Tongkat ali may boost low testosterone, combat anxiety, and improve body composition, but research is limited. Check with your healthcare provider before taking this supplement.

Tongkat ali, or longjack, is an herbal supplement suggested to improve low testosterone, male fertility, anxiety, athletic performance, and muscle mass.

Still, research is limited.

If you’re interested in trying tongkat ali, talk to your healthcare provider and look for a reputable brand in stores or online.