Tongkat ali
Supplement
botanical
men's healthfitness
Not medical advice. Check with your doctor or pharmacist before you start, stop or change the timing of anything you take.
How to use
What it’s for
Total testosterone in men — 5 small RCTS pooled
When to take
Timing untested
Studied for
Trials dose daily for 2 weeks to 6 months
Pros & cons
Pros
- Pooled testosterone rise across 5 RCTS (smd 1.35)
- Trials used 100–600 mg a day of one standard extract
- Only one trial reported side effects
Cons
- 87% heterogeneity and signs of publication bias
- Malaysian survey: some products had no eurycomanone
- Small, short trials; mostly one proprietary extract
Sources
- Eurycoma longifolia (Jack) Improves Serum Total Testosterone in Men: A Systematic Review and Meta-Analysis of Clinical Trials (Leisegang et al., Medicina 2022) · read 2026-08-27
what it says
“The random model effect revealed a significant increase (SMD = 1.352, 95% CI 0.565 to 2.138, p = 0.001) in the total testosterone levels in men receiving E. longifolia supplementation”
- Leisegang et al. 2022 — studies included and population · read 2026-08-27
what it says
“a total of nine studies was included in the systematic review. Five RCTs were included in the meta-analysis … Five eligible RCTs measuring the testosterone levels in men (n = 232)”
- Leisegang et al. 2022 — Table 1, supplement dosage and treatment length · read 2026-08-27
what it says
“Physta, Biotropics 600 mg/day for 2 weeks … Dry extract 200 mg up to 6 months … 100 mg/daily up to 12 weeks … 200 mg/daily up to 12 weeks … 300 mg for 12 weeks”
- Leisegang et al. 2022 — reported adverse effects · read 2026-08-27
what it says
“Only one study reported adverse effects associated with E. longifolia treatment, which included gastrointestinal symptoms and itching, while Ismael et al. observed adverse events in both treated and placebo groups”
- Leisegang et al. 2022 — heterogeneity and publication bias · read 2026-08-27
what it says
“Tests for heterogeneity implicated heterogeneity across the five studies … with 87.27% inconsistency … a low p value (0.0243) was noticed with Begg's test, indicating publication bias”
- Leisegang et al. 2022 — eurycomanone content of marketed products · read 2026-08-27
what it says
“Out of 41 products containing E. longifolia as a single or compound formulation from Malaysia, 24 products contained eurycomanone: 11/24 reached the recommended levels, while 9 were above the recommended levels … Some products did not contain any eurycomanone”
- Leisegang et al. 2022 — stated limitations · read 2026-08-27
what it says
“the analysis was based on five studies, which were heterogeneous in terms of study design, included population, dosage and length of treatment, and limited sample sizes”
- HSA — Guidelines on Prohibited and Restricted Ingredients in Health Supplements and Traditional Medicines, GL-CHPB-1-012 Rev 001 (Oct 2025), Annexes A and B — Eurycoma longifolia / tongkat ali / longjack not listed in Annex A or B (full text searched) · read 2026-08-27
what it says
“The objective of this guideline is to highlight the substances of concern when used in HS and TM and is not meant to be an exhaustive list.”
- iHerb Singapore — Tongkat Ali category page, default (best-selling) order, SGD pricing; no Singapore shipping-restriction notice shown · read 2026-08-27
what it says
“Solaray, Tongkat Ali, 400 mg, 60 VegCaps … Nutricost, Tongkat Ali, 120 Capsules … Swanson Vitamins, Tongkat Ali, 400 mg … Nature's Truth, Longjack Tongkat Ali … NOW Foods, TestoJack 200”
Updated 2026-08-29. Every line above traces to a numbered source. Kozen-X is not a medical device and does not give medical advice. It lists what published sources have written down — nothing more. A pair not listed is unrecorded, not cleared. Before you start, stop or re-time anything, talk to your doctor or pharmacist.