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Tribulus Terrestris Update
Richard B. Kreider, PhD, FACSM

I recently came across a web site promoting the ergogenic value Tribulus terrestris. The site claimed that
Tribulus supplementation would naturally boost testosterone levels leading to greater gains in muscle
mass and strength during training. Is this true? This article discusses what we know and dont know
about Tribulus terrestris so you can make an informed decision of whether to add this supplement to your
training table.

Background
Tribulus terrestris is a plant (also known as puncture weed/vine or caltrops) that is mainly grown in sandy
soil environments. It produces a fruit that is protected by a spiny burr. The extract from the fruit has
been used in herbal medicine as a diuretic, for colic pains, and to fight hypertension and
hypercholesterolemia (1,2). It has also been shown to increase testosterone levels (3) and improve sexual
function in animals (3-5) as well as to reduce symptoms of angina pectoris in heart patients (6).
Excessive intake of Tribulus terrestris has been reported to cause neuromuscular disorders in sheep (7-8).
The active agent in Tribulus is believed to be protodioscin. Protodioscin is a precursor to
dehydroepiandrosterone (DHEA). As you may know, DHEA and androstenedione are precursors to
testosterone. As one ages, androgen levels decline. Therefore, DHEA and androstenedione
supplementation have been theorized as a means of naturally increasing testoserone levels particularly in
older individuals. Although Tribulus is a precursor to DHEA, Tribulus is believed to indirectly affect
testosterone levels by stimulating the release of leutinizing hormone (LH). LH serves to stimulate the
natural production of testosterone. Theoretically, moderately increasing testosterone availability during
training may promote greater gains in strength and muscle mass.

Does Tribulus Terrestris Work?
Well, as you know, the theoretical rationale behind many supplements sounds promising. However, the
promises often fade when one looks at the scientific evidence supporting the theories. Tribulus is no
exception. To date, there are only a handful of studies that have investigated the effects of Tribulus
terrestris supplementation on hormone regulation, sexual function, health, and/or training adaptations.
Most of these studies have been conducted in animals. Although several web sites claim that Tribulus
terrestris supplementation markedly increases LH and testosterone levels, I was only able to find two
published studies that have investigated the effects of Tribulus terrestris supplementation on training
adaptations in humans.

In the first study, Antonio and colleagues (9) evaluated the effects of Tribulus terrestris supplementation
during training on body composition and performance. In a double blind and randomized manner, 15
resistance-trained males ingested either 3.21 mg/kg/day of a placebo (P) or Tribulus terrestris (T) for eight
weeks during a standardized resistance-training program. Prior to and following supplementation,
subjects completed dietary inventories, a mood state psychological inventory, and had body composition
(skinfolds and hydrostatic weighing) and total body water (bioelectrical impedance) measurements
determined. The subjects also performed a maximum repetition tests on the bench press and leg press at
100% and 200% of body weight, respectively. Results revealed that Tribulus terrestris supplementation
had no significant effects on changes in mood states, total body weight (P +0.6, T +0.9 kg), total body
water (P +0.9, T +0.3 liters), hydrostatically determined percent body fat (P +0.2, T +0.0 %), or gains in
bench press (P +28.4, T +3.1 %) or leg press (P +26.1, T +28.6 %) muscle endurance. Although LH and
testosterone levels were not assessed in this study, results indicated that Tribulus terrestris
supplementation (approximately 250 mg/day) during resistance training had no significant effects on body
composition or training adaptations.

Proponents of Tribulus terrestris supplementation have suggested that the dosage in the previous study
may have been insufficient, that Tribulus terrestris may be more effective when coingested with other
anabolic precursors, and/or that Tribulus terrestris may have a greater impact on untrained subjects
initiating training. However, research findings from a study by Brown and associates (10) do not support
these contentions. In the first part of this study, 10 subjects were evaluated to determine the effects of
ingesting a placebo or anabolic precursors on hormone levels. Subjects had fasting blood determined and
then ingested a placebo or a supplement containing 100 mg androstenedione, 50 mg DHEA, 250 mg
Tribulus terrestris, 195 mg Chrysin, 100 mg Indole-3-carbinol, and 180 mg Saw palmetto. Blood samples
were obtained every hour for six hours. Results revealed that anabolic precursor supplementation
significantly increased androstenedione levels. However, no significant differences were between the
placebo and anabolic precursor trials in LH, follicle stimulating hormone (FSH), estradiol, free
testosterone, or total testosterone levels. These findings suggest that although anabolic precursors may
increase androstenedione levels, they have no significant acute effect on other androgenic or estrogenic
hormones.

In the second phase of this study, 20 untrained young male subjects participated in a 3-day per week
resistance training program for 8-weeks. In a double blind and randomized manner, subjects ingested a
placebo (P) or a supplement containing 300 mg androstenedione, 150 mg DHEA, 750 mg Tribulus
terrestris, 625 mg Chrysin, 300 mg Indole-3-carbinol, and 540 mg Saw palmetto (Andro-6) every day
during weeks 1, 2, 4, 5, 7, and 8 of training. Fasting blood samples were obtained prior to
supplementation and after 2, 5, and 8 weeks of supplementation. Body composition (via skinfolds and
hydrostatic weighing) and one-repetition maximum (1RM) upper and lower body strength tests were
determined at 0, 4, and 8 weeks of supplementation. In addition, muscle biopsies were obtained prior to
and following the supplementation/training interventions to assess changes in muscle fiber diameter.
Results revealed that chronic Andro-6 supplementation during training increased fasting androstenedione,
estradiol, and estrone levels while decreasing high-density lipoproteins (HDL) levels. No significant
differences were observed in LH, FSH, total testosterone, free testosterone, or estriol levels. Moreover,
no significant differences were observed between groups in changes in body composition, muscle fiber
diameter, or gains in 1RM strength. These findings suggest that ingesting Tribulus terrestris (750
mg/day) with other anabolic precursors does not significantly affect body composition or training
adaptations.

Bottom Line
Despite popular claims, there currently appears to be little if any data supporting the ergogenic value of
Tribulus terrestris supplementation for resistance-trained athletes. Additionally, studies that have
evaluated the ergogenic value of other anabolic precursors in younger athletes have shown little to no
benefit with some potentially dangerous side effects. My advice is to stay away from these types of
anabolic precursors unless recommended by your physician.