Supplement analysis backed by scientific evidence · PT

← All supplements
Limited evidenceMen's health

D-Aspartic Acid

D-aspartic acid is sold as a natural testosterone booster on the strength of one small 2009 study that later, better-controlled trials failed to replicate. In resistance-trained men the good evidence is uniformly null — and at 6 g/day it may actually lower testosterone.

What the science says

  • Raising testosterone in resistance-trained men Limited evidence

    Willoughby's randomised trial gave 3 g/day for 28 days alongside heavy resistance training and found no effect on total or free testosterone, body composition or strength. Melville's 2015 trial went further: 6 g/day significantly decreased total and free testosterone, while 3 g/day did nothing. The original positive finding was in untrained men with low baseline testosterone and has not replicated in trained populations.

  • Increasing muscle mass and strength Limited evidence

    Melville's 2017 three-month randomised controlled trial in resistance-trained men found no significant benefit of D-aspartic acid on body composition, muscle mass or strength versus placebo. Combined with Willoughby's 28-day null result, this is about as clean a negative as sports supplement literature offers.

  • Male fertility and sperm parameters Limited evidence

    Some small trials, often using D-aspartic acid in combination formulas with zinc and ubiquinol, report improvements in semen parameters in men with idiopathic infertility. Because these are combination products, the contribution of D-aspartic acid specifically cannot be isolated.

Dosage & safety

Studied doseStudies have used 3 g/day and 6 g/day for 14-90 days. Given that 6 g/day suppressed testosterone in one trial and 3 g/day did nothing in two, there is no dose we can recommend for testosterone support.
SafetyShort-term trials report few adverse effects beyond occasional headache, irritability and GI upset, but long-term safety data are essentially absent. The suppression of testosterone at 6 g/day is itself a safety signal, plausibly via negative feedback or downregulation of testicular D-aspartate oxidase. Not recommended for men with hormone-sensitive conditions, for anyone under 18, or in pregnancy. Not a WADA-prohibited substance, but products marketed as testosterone boosters are a common source of undeclared steroid contamination — a real doping risk for tested athletes.

Scientific references

Where to buy

ALLMAX, D-Aspartic Acid, 3.53 oz (100 g)

View on iHerb

Referral link — this site may earn a commission on purchases.

Related in Men's health