Walk into any supplement aisle and you'll find Tribulus terrestris promising big strength and muscle gains in as little as 5 to 28 days. So what happened when researchers put it to the test on elite rugby league players doing brutal preseason training? Nothing. Not a thing that beat a sugar pill.
The study, published in the Journal of Strength and Conditioning Research in 2007, remains a handy reality check for anyone tempted by a "natural testosterone booster."
The Claim: Big Gains in Under a Month
Tribulus terrestris is an herbal supplement marketed to athletes and lifters. According to the paper, it is promoted to produce large gains in strength and lean muscle mass within 5 to 28 days. That is an extraordinary promise for any legal supplement.
There was a second angle too. Some manufacturers say Tribulus won't cause a positive drug test, while others have suggested it might raise the urinary testosterone/epitestosterone (T/E) ratio, which could put tested athletes at risk. The researchers set out to examine both questions: does it build strength and muscle, and does it trip the doping flag?
How the Study Worked
The design was strong for a supplement trial:
- Type: Randomized, double-blind, placebo-controlled, match-paired trial
- Participants: 22 elite Australian male rugby league players (average age 19.8 ± 2.9 years, average weight 88.0 ± 9.5 kg)
- Groups: 11 players took Tribulus terrestris; 11 took a placebo
- Dose: 450 mg per day of Tribulus terrestris extract, taken once daily
- Duration: 5 weeks
- Training: All players followed structured heavy resistance training as part of their club's preseason preparation
The researchers measured muscular strength, body composition (including fat-free mass) and the urinary T/E ratio before and after the supplementation period.
The Result: Everyone Got Stronger, Tribulus Didn't Help
Here's the twist. Strength and fat-free mass did increase significantly over the five weeks. But they went up in both groups, and there were no differences between the Tribulus and placebo groups.
In other words, the gains came from the heavy training, not from the capsule. The players who took a placebo got the same benefits as those taking the herbal extract. The authors concluded that Tribulus terrestris did not produce the large gains in strength or lean muscle mass that many manufacturers claim can occur within 5 to 28 days.
This is a classic example of why placebo controls matter. Without them, the Tribulus group's improvement might have been hailed as proof the product works.
The Doping Question: No Change in T/E Ratio
The second finding matters for tested athletes. The urinary T/E ratio showed no between-group differences. The authors concluded Tribulus would not place an athlete at risk of testing positive based on the World Anti-Doping Agency's T/E limit of 4:1.
That's reassuring from a compliance standpoint, but it also quietly reinforces the main finding. If the supplement doesn't shift the T/E ratio, it's not behaving like a meaningful testosterone booster in this population. Note that the supplement-contamination risk common to the wider industry is a separate issue and wasn't what this study examined.
Limits You Should Know About
Good science means being honest about what a study can't tell us:
- Small sample: Only 22 athletes, 11 per group. Small trials can miss subtle effects.
- Single dose: Only 450 mg/day of one extract was tested. Other doses or formulations weren't evaluated.
- Short duration: Five weeks is brief, though it covers the window manufacturers claim results appear.
- Specific population: Young, elite, well-trained male rugby players in heavy preseason training. Results may differ in older men, women or untrained people.
- Hard-training context: A big training stimulus can mask small supplement effects.
Still, the claim being tested was for large gains in a matter of weeks. This study found no sign of that.
What This Means for You
Dose and timing: The study used 450 mg/day of Tribulus extract once daily for 5 weeks, and it showed no benefit over placebo. There is no dose or timing from this paper that we can recommend for results.
Who might still be curious: Anyone tempted by the "natural testosterone booster" label should know this trial gives them no evidence for strength or muscle gains. Tested athletes can take some comfort that the T/E ratio didn't move, but that's not a reason to buy it.
Who should skip it: If your goal is more strength, muscle or better performance, skip it. That's especially true if your budget is limited or you're already training hard and getting results.
Where to put your money instead: Spend it on options with a far stronger evidence base:
- Creatine for strength, power and lean mass support
- Protein to help you hit daily intake targets for muscle repair and growth
- A well-structured resistance program, sleep and enough total calories
As this trial showed, consistent heavy training did the heavy lifting. Both groups got stronger and leaner-mass heavier without any help from the herbal extract.
Bottom Line
In a double-blind trial of 22 elite rugby league players, 450 mg/day of Tribulus terrestris for five weeks delivered no advantage over placebo for strength, fat-free mass or the T/E ratio. With only one dose tested and a small sample, it isn't the final word, but it's a strong reason to be skeptical of the hype. Save your cash for what's proven.
