Tongkat Ali, or Eurycoma longifolia, is a root from a green shrub tree native to Southeast Asian countries like Malaysia, Indonesia, and Vietnam. This traditional herb has been used for centuries in local medicine for its perceived effects on vitality and general well-being. Modern interest centers on its potential as a performance-enhancing supplement for boosting physical strength and increasing muscle mass. This popularity has led many to search for scientific confirmation of its muscle-building properties.
The Proposed Mechanism: Testosterone and Cortisol
The theoretical benefit of Tongkat Ali for muscle growth stems from its interaction with two primary hormones: testosterone and cortisol. The root extract contains bioactive compounds called quassinoids, with eurycomanone being the most well-known. These compounds influence the hormonal environment, creating a more favorable state for anabolism (muscle building).
Tongkat Ali may help the body manage stress, and supplementation has been shown to reduce levels of the stress hormone cortisol in some studies. Since cortisol is catabolic and breaks down muscle, lowering it indirectly supports muscle maintenance and growth.
The herb is also believed to support higher levels of free testosterone, the form readily available for biological action. Quassinoids may achieve this by interfering with Sex Hormone-Binding Globulin (SHBG), a protein that binds to testosterone and renders it inactive. Evidence suggests that eurycomanone may also inhibit the aromatase enzyme, which converts testosterone into estrogen. This increases active testosterone and reduces catabolic hormones, favoring muscle growth and recovery.
Clinical Evidence for Muscle and Strength Gains
Research investigating Tongkat Ali’s effect on muscle mass and strength has yielded mixed but often promising results. Clinical trials have measured metrics like lean body mass (LBM) and maximal strength (1-RM). One study involving young men undergoing intensive weight training found that 100 mg of extract daily over eight weeks led to greater improvements in LBM, arm circumference, and 1-RM strength compared to the placebo group.
Positive findings were also observed in older populations, suggesting the herb may help mitigate age-related muscle decline. A study on active older adults supplementing with 400 mg daily for five weeks demonstrated a significant increase in muscular strength over the placebo group. Another trial in older men with clinically low testosterone levels showed that 200 mg daily resulted in increased muscle strength after 12 weeks.
However, the evidence is not universally positive. A trial on exercise-trained males and females taking 400 mg daily for four weeks showed no significant differences in body composition, including LBM or fat mass, compared to placebo. Similarly, a study on middle-aged women found that 100 mg of the supplement did not enhance strength gains beyond the benefits of the exercise itself. These conflicting results indicate that the ergogenic effect may depend on the individual’s age, training status, dosage, and initial hormonal profile.
Safety Profile and Dosage Considerations
Research suggests that a daily intake between 200 mg and 400 mg of a standardized extract is generally acceptable for adults. Some studies have safely utilized doses up to 600 mg daily for short periods, and intakes up to 1,200 mg per day have been deemed safe in certain toxicity assessments.
Reported side effects are usually minor and may include mild gastrointestinal upset, itching, restlessness, anxiety, or insomnia. Individuals with pre-existing hormone-sensitive conditions, such as certain cancers, or those with heart, liver, or kidney disease, should exercise caution.
A significant safety concern relates to product quality and regulation. As a dietary supplement, Tongkat Ali is not strictly regulated, leading to a high risk of contamination. The root can absorb heavy metals from the soil, and reports have identified contamination with lead, mercury, cadmium, and arsenic. Consumers should look for products that specify a standardized extract and have been verified by reputable third-party testing organizations to ensure purity and accurate labeling.