D-Aspartic Acid

In a randomized, double-blind, placebo-controlled 14-day trial in 24 resistance-trained men (8 per arm), D-aspartic acid did not increase testosterone: total testosterone fell about 12.5% in the 6 g/day arm (P=.03) and free testosterone fell versus placebo (P=.005), while the 3 g/day arm showed no significant change. An earlier 12-day study in a different, non-resistance-trained population reported increases, so a general testosterone-boosting claim is unsupported.^[1][2]

• Small (n=8 per arm) 14-day trial; results differ from an earlier study in a different population and do not establish recovery after anabolic-androgenic steroid use.
• Full-text-checked; no qualified clinical review.

An earlier study, whose human groups were not described as randomly assigned, reported that 12 days of oral sodium D-aspartate in 23 men raised serum LH by 33% and testosterone from 4.5 to 6.4 ng/mL (both P<.001), with no change in 20 placebo recipients. A later randomized, double-blind trial in resistance-trained men found no such increase, and a decrease at a higher dose, so this result should not be presented as a reliable effect across populations.^[2][1]

• The human groups were not described as randomly assigned, and separate rat/isolated-pituitary/Leydig-cell mechanistic experiments cannot establish the human mechanism; results conflict with a later randomized trial in resistance-trained men.
• Full-text-checked; no qualified clinical review.