Tongkat ali (Eurycoma longifolia), also known as longjack or Malaysian ginseng (unrelated to Panax ginseng), is an herb from Southeast Asia. The extract of the roots of the plant has been traditionally used to enhance testosterone levels in men, though it has also been proposed to be able to reduce blood pressure, fever, and fatigue. Unfortunately, there’s scant evidence to support these effects.^[1] Furthermore, the internet is full of low-quality information about tongkat ali.^[2]

The main bioactive components in tongkat ali are the quassinoid compounds (eurycomanone and eurycomanol), eurycolactones, canthin-6-one metabolites, eurylene and teurilene (derivatives of squalene), and eurypeptides.

Tongkat ali has mainly been studied for its use as an aphrodisiac. However, the mechanisms by which tongkat ali may enhance aphrodisia are not well understood, and most of the research has been conducted in animals. This effect seems to be based in lore and tradition rather than hard evidence.

Supplementation may increase total testosterone in healthy and hypogonadal men, improve erectile function and alleviate symptoms of erectile dysfunction, increase fertility, and enhance sexual function and well-being.^[3][4][5] One study found evidence of an anxiolytic (anxiety and stress-reducing) effect of tongkat ali.^[6] It should be noted that evidence for these outcomes is somewhat limited given the lack of published randomized controlled trials in humans.

There is sparse safety, quality, and toxicity data available for tongkat ali from human studies, along with a lack of standard criteria and regulation for its commercial preparations. Some studies have raised concerns about the possible contamination of herbal preparations of tongkat ali by heavy metals in Malaysia, including levels of lead and mercury above permissible limits.^[7][8][9]

Safety and toxicity studies in rodents have found that the LD₅₀ for tongkat ali (the dose that, when administered all at once, causes death in 50% of test animals) is greater than 3,000 mg/kg for the aqueous extract and between 1,500–2,000 mg/kg for the alcoholic extract.^[10] Pathological changes in the liver were observed in rats at a dose of 1,200 mg/kg, corresponding to a 1,200 mg daily dose in humans.^[11] However, tongkat ali has been shown to be safe for the liver in humans.^[3]

Studies using a dosage of 200–600 mg/day in humans have noted minor side effects, including gastrointestinal symptoms and itching.^[3] Otherwise, adverse effects seem to be rare.^[4] Tongkat ali is not recommended for pregnant and lactating women; men with breast or prostate cancer, diabetes, heart disease, kidney disease, liver disease, or sleep apnea; and children, due to a lack of data in these populations.^[12][13]

Tongkat ali may impede the actions of propranolol, a medication used to treat high blood pressure (hypertension), by interfering with its absorption and bioavailability.^[14] Anyone using this medication and considering supplementing with tongkat ali should first consult a healthcare professional.

Tongat ali’s effects on male sexual enhancement are primarily attributed to eurycomanone, which has steroidogenic activity. Eurycomanone has been shown to have anti-estrogenic effects. It inhibits the aromatase enzyme and prevents the conversion of testosterone to estrogen in the Leydig cells of the testes, the primary site of sperm production in men.

At higher doses, eurycomanone may inhibit phosphodiesterase (PDE) activity, resulting in an accumulation of cyclic AMP, an increase in cholesterol transport, and an increased production of pregnenolone, a precursor for testosterone biosynthesis.^[15] Furthermore, activation of the CYP17a enzyme by eurycomanone increased production of testosterone precursors DHEA and androstenedione.^[16] Tongkat ali may enhance sperm production by increasing the production of the gonadotropins luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which elevate testosterone and sperm production in the testes, respectively.^[17]