Chan KQ, Stewart C, Chester N, Hamzah SH. The effect of Eurycoma longifolia on the regulation of reproductive hormones in young males. Andrologia. May 2021;53(4):e14001. doi: 10.1111/and.14001.

Tongkat ali (Eurycoma longifolia, Simaroubaceae) contains bioactive compounds that increase testosterone levels in hypogonadal older adults; however, little is known about the effect of tongkat ali on the activation of the hypothalamic-pituitary-gonadal (HPG) and hypothalamic-pituitary-adrenal (HPA) axis in younger adults. Therefore, the purpose of this placebo-controlled, double-blind study was to assess the impact of tongkat ali on the HPG axis in healthy young males.

Thirty-two healthy collegiate males aged 18-30 years with no diagnosis of low testosterone levels or hypogonadism were recruited for the study. The participants were evenly randomized to receive 600 mg of tongkat ali (Physta^®; Biotropics Malaysia, Berhad; Shah Alam, Selangor, Malaysia) or a placebo containing maltodextrin for two weeks. Resting heart rate, blood pressure, and anthropometric measurements were collected at two visits — pre- (day 1) and post-intervention (day 14). The participants were instructed to fast and refrain from alcohol, performance enhancing supplements, high-intensity exercise, and sexual activity for eight hours before each lab visit. The participants completed a 24-hour diet recall and physical activity questionnaire on day 1 and were asked to replicate the same diet and physical activity through day 14.

All participants completed the study with 100% compliance (n = 16 in both groups). There were no significant differences between the groups at baseline for age, body weight, or body composition. Participants who received tongkat ali demonstrated a significant 15% (P = 0.001) and 34% (P = 0.004) increase in total and free testosterone, respectively, following two weeks of supplementation compared with placebo. Estradiol was also significantly increased by 30% (P = 0.006) after two weeks of tongkat ali supplementation compared with placebo. There were no inter or intra significant differences between the groups for luteinizing hormone (LH), follicle stimulating hormone (FSH), or sexual hormone-binding globulin. No adverse effects were reported.

Based on their findings, the authors conclude that a standardized dosage of 600 mg of tongkat ali increased testosterone levels and demonstrated steroidogenic effects in young males. Levels of LH an FSH showed no significant changes with tongkat ali supplementation, suggesting an unclear impact on the HPG axis and the involvement of the HPA axis in increasing testosterone levels . While the authors did not discuss potential limitations to their study, they did not specify whether the two blood samples were obtained at the same time of day to reduce measurement errors caused by hormone fluctuations.

To the authors' knowledge, no study has investigated the effect of a tongkat ali dose greater than 400 mg on testosterone production in young adults. Since this study is the first to demonstrate a significant increase in testosterone and estradiol levels in healthy young males, further investigation is needed to understand the associated mechanisms. While not suggested by the authors, future trials may also consider a longer intervention period with follow-up to determine whether the increases in testosterone and estradiol are maintained and what effect tongkat ali supplementation has on hormone levels when combined with resistance training. Additionally, while testosterone levels are correlated with muscle strength and size, the number of androgen receptors a person has may be a better determinant for muscle growth. The authors report no conflicts of interest.

–Gavin Van De Walle, MS, RDN