Independent supplement ratingsUS and Canada · Updated weekly
A ratings desk for a category that has spent thirty years grading its own homework.
A ratings desk for a category that has spent thirty years grading its own homework.
One 2009 study in untrained men launched a shelf full of products. Three trials in the men who actually buy them found nothing, and one found the opposite.
The short version: D-aspartic acid is the reason testosterone boosters exist as a shelf category. An early study reported a rise in testosterone, the industry moved in within months, and the ingredient is still printed on labels today. It has since been tested three times in resistance-trained men — the people the products are sold to — and it did nothing. In one trial it moved testosterone the wrong way.
DAA is an amino acid involved in the signalling that leads to testosterone release. The mechanism is real. In 2009 a study gave 23 men a daily dose for twelve days, against 20 on placebo, and reported a rise in testosterone. (Topo et al., 2009)
Twenty-three men. Twelve days. In a market waiting for exactly that headline, one plausible mechanism and one small short study were enough, and products followed almost immediately.
That sequence — mechanism, single study, shelf — is the standard path in this business, and it runs faster than replication does.
Three randomised trials looked at DAA in resistance-trained men. All three point the same way.
2013. Twenty-eight days of heavy resistance training with DAA supplementation produced no effect on body composition, muscle strength or testosterone. (Willoughby & Leutholtz, 2013)
2015. Researchers gave resistance-trained men three grams and six grams a day, testing whether more would do what less had not. Testosterone did not rise. In the six-gram group it fell. (Melville, Siegler & Marshall, 2015)
2017. The most complete test: a randomised, double-blind, placebo-controlled trial over twelve weeks, with 6 g a day and a supervised four-day-a-week programme. Measurements covered total and free testosterone, oestradiol, SHBG, isometric strength, and muscle cross-sectional area by ultrasound.
Result: no change in total or free testosterone. Strength and hypertrophy gains identical to placebo. The authors' conclusion runs to a single line — DAA supplementation is ineffective at changing testosterone levels or positively affecting training outcomes. (Melville, Siegler & Marshall, 2017)
Not because anyone cheated. Two ordinary reasons cover it.
The population changed. The early work was in untrained men. Every later trial used resistance-trained men, who have adapted hormonal responses and, on average, less room to move. An effect in one group is not a promise in the other, and the products are aimed squarely at the second.
Single small studies are unreliable, in both directions. A first positive result is a reason to run a bigger trial, not a reason to build a product line. When the bigger trials arrived, they disagreed. That is replication doing its job.
The failure is not that the first study existed. It is that an industry was built on it and did not dismantle itself when the follow-ups came in.
Nine years after the twelve-week trial, DAA is still sold. One product in our own testosterone ranking is built around it, carrying 2,300 mg per serving at over two dollars a serving — a clean, disclosed, checkable dose of an ingredient the better trials could not make work.
That is worth separating out, because it is not the same sin as hiding a formula. Full disclosure of an ingredient that failed is more honest than a proprietary blend, and it is still not a reason to buy. Our full read on that product is in the review.
DAA is a template, and the next one will look identical. Four questions catch it early:
We keep the running record for this ingredient on its page, and the wider category audit — where 61.5% of ingredients had no published data at all — is in do testosterone boosters work.
Educational only, not medical advice. If you think your testosterone is low, that is a blood test and a doctor, not a shelf.