D-Aspartic Acid and Testosterone: What Studies Show

In short: D-aspartic acid is an amino acid your body makes on its own and uses in hormone signaling. One small 2009 study found it raised testosterone in inactive men after 12 days, which is why it’s in so many “testosterone boosters.” But every later trial in men who lift weights found no rise in testosterone, no extra muscle and no extra strength, and one found that a high 6-gram dose actually lowered testosterone.

D-aspartic acid (often shortened to DAA or D-Asp) sits near the top of the label on many testosterone boosters. The pitch sounds scientific: it’s involved in the chain of signals that tells your body to make testosterone, so taking more should mean more testosterone. Here’s what the studies in real people actually show, who they were done in, and whether D-aspartic acid is worth your money.

What is D-aspartic acid?

Most amino acids come in two mirror-image forms, called “L” and “D.” The L form of aspartic acid is a common building block of protein. The D form is different: it isn’t used to build protein, but it does act as a signaling molecule in the brain and hormone glands.

Your body makes D-aspartic acid itself, using an enzyme that converts ordinary L-aspartic acid into the D form. In rats, the highest levels are found in the pituitary gland (the “master gland” at the base of the brain) and the testes [1]. It’s also found in the pineal gland, the small gland that makes melatonin [3]. Small amounts of D-amino acids also turn up in food, especially foods that have been heated, treated with acid or alkali, or fermented [2].

How D-aspartic acid is supposed to raise testosterone

Testosterone production is controlled by a chain of signals often called the HPG axis (hypothalamus, pituitary, gonads). The hypothalamus in the brain releases a hormone that tells the pituitary to release luteinizing hormone (LH). LH then travels in the blood to the testes and tells them to make testosterone.

In rat studies, D-aspartic acid acts at several points in this chain. It boosted the release of the brain’s LH-triggering hormone in rat hypothalamus tissue [4], increased LH made by isolated rat pituitary glands, and increased testosterone made by rat testicular cells in a dish [1]. A 2017 systematic review counted 23 animal studies and concluded that extra D-aspartic acid does raise testosterone in male animals [5]. The big question is whether that carries over to people.

Does D-aspartic acid raise testosterone in men?

The study that started the hype

In a 2009 Italian study, 23 healthy men aged 27–37 drank 3.12 grams of sodium D-aspartate a day (as a product called DADAVIT, which also contained vitamins B6, B12 and folic acid) for 12 days, while 20 men took a placebo. Testosterone rose by an average of 42% (from 4.5 to 6.4 ng/mL) and LH by 33% in the D-aspartic acid group, and nothing changed with placebo [1].

That sounds impressive, but the study had real weaknesses. The men were recruited at a fertility clinic, little was reported about them apart from their age, it wasn’t clear that they were randomly assigned to groups, and their starting testosterone was in the lower part of the normal range [5]. It also lasted less than two weeks. Even after the rise, their levels were still in the middle of the normal range.

Studies in men who lift weights

Testosterone boosters are mostly sold to gym-goers, so the more relevant studies are the ones done in trained men. They tell a very different story.

• 28 days, 3 grams a day (20 men): in a randomized, double-blind trial in resistance-trained men, D-aspartic acid didn’t change total or free testosterone, LH or estradiol (a form of estrogen). Both groups gained similar strength and muscle from training [6].
• 14 days, 3 or 6 grams a day (24 men): 3 grams had no effect on testosterone. 6 grams lowered total and free testosterone compared with the start of the study [7].
• 12 weeks, 6 grams a day (22 men): in the longest trial so far, testosterone didn’t change in either direction. Both groups got stronger and built similar amounts of muscle [8].
• 2 weeks, 3 grams a day (16 male climbers): no change in testosterone, LH or physical performance compared with placebo [9].
• 14 days, 6 grams a day (16 male boxers): no effect on testosterone, LH or cortisol during an altitude training camp [10].

An open-label study (no placebo, and everyone knew what they were taking) of a D-aspartic acid blend with sodium nitrate and vitamin D3, in 10 overweight or obese men around age 42 with lowish testosterone, also found no significant rise [5]. That’s worth noting, because one popular explanation is that D-aspartic acid only works when testosterone starts out low.

Why the difference from the 2009 study? Nobody knows for sure. Differences in the men studied, their training and their starting hormone levels are possible explanations [5]. In the 28-day trial, the men taking D-aspartic acid had higher levels of the enzyme that breaks it down, which suggests the body may simply clear the extra amount [6]. That’s an idea, not a proven explanation.

What the reviews conclude

The 2017 systematic review found that human results were “inconsistent” and that the evidence in men was “still sparse,” mostly because of the small number and low quality of the studies [5]. A broader 2023 systematic review of 27 so-called testosterone boosters found that most failed to raise total testosterone compared with placebo, and D-aspartic acid wasn’t among the few exceptions [12].

D-aspartic acid for muscle and strength

Even if D-aspartic acid did nudge testosterone up a little within the normal range, that wouldn’t necessarily mean more muscle. And in the trials that measured it, it didn’t: men taking D-aspartic acid gained the same strength and muscle as men on placebo, over 4 weeks [6] and 12 weeks [8]. The climbers showed no change in physical performance either [9].

The related compound NMDA (N-methyl-D-aspartate, which the body can make from D-aspartic acid) has also been sold as a testosterone booster. A 28-day trial in 20 resistance-trained men found it had no effect on testosterone, other hormones, muscle or strength [11].

D-aspartic acid and male fertility

D-aspartic acid was first marketed in Italy to improve sperm quality, and fertility is where the research is moving. In a 2025 randomized, placebo-controlled trial, men with unexplained infertility took 2,660 mg of D-aspartic acid plus 200 mg of ubiquinol (a form of CoQ10) and 10 mg of zinc daily for 3 months (24 men per group). Sperm movement and testosterone both improved modestly compared with their starting values [13].

Because three ingredients were given together, this study can’t tell us how much (if any) of the benefit came from D-aspartic acid itself. It also didn’t report pregnancies. If you’re trying to conceive, it’s worth talking to a fertility specialist rather than relying on a supplement.

Estrogen and nerve signaling

Some websites claim D-aspartic acid raises estrogen. In trained men, the 28-day trial found no change in estradiol [6], and the 12-week trial found estradiol fell by about 16% with 6 grams a day [8].

The 12-week trial also tested reflexes in the calf. The placebo group’s spinal reflex responses improved with training, while the D-aspartic acid group didn’t show that improvement. The researchers described this as a “blunting” of nerve responsiveness that didn’t seem to affect strength gains [8]. It’s a single small finding, and what it means in practice is unknown.

Dose, side effects and safety

Studies have used 2.6 to 6 grams a day, for 12 days to 3 months. There’s no official recommended dose, and the one trial that compared doses found that the higher 6-gram dose lowered testosterone over two weeks [7].

Most trials reported few problems, but they were small and short. In the 28-day trial, three men reported irritability, nervousness, a fast heart rate or headache [5]. The 2017 review pointed out that it isn’t clear whether the doses used are safe for people long term, and that very high amounts caused signs of oxidative stress in some animal tissues [5]. No studies have looked at use beyond about 3 months.

Also keep in mind that D-aspartic acid is usually sold inside multi-ingredient “boosters,” which can contain stimulants or herbs with their own side effects. If you have a hormone condition, take any medicines, or are being treated for low testosterone or infertility, check with your doctor first.

If you’re curious about other popular testosterone supplements, see what the research says about whether ZMA works, ashwagandha and whether ginger increases testosterone.

The bottom line on D-aspartic acid

D-aspartic acid plays a real role in hormone signaling, and it raises testosterone in animals. In people, one small, short study in inactive men found a rise, but five trials in men who train found no increase in testosterone, muscle or strength, and a high 6-gram dose lowered testosterone in one of them. Early fertility research is interesting but tested D-aspartic acid mixed with other ingredients. For most gym-goers, consistent training, enough protein and good sleep will do far more than D-aspartic acid.

This article is for general information only and isn’t medical advice. Talk to your doctor or another qualified health professional before starting a new supplement. See our medical disclaimer.

References

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2. Genchi G. An overview on D-amino acids. Amino Acids. 2017;49(9):1521-1533. doi:10.1007/s00726-017-2459-5
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4. Pampillo M, Scimonelli T, Bottino MC, et al. The effect of D-aspartate on luteinizing hormone-releasing hormone, alpha-melanocyte-stimulating hormone, GABA and dopamine release. Neuroreport. 2002;13(17):2341-2344. doi:10.1097/00001756-200212030-00034
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9. Crewther B, Witek K, Draga P, et al. Short-term d-aspartic acid supplementation does not affect serum biomarkers associated with the hypothalamic-pituitary-gonadal axis in male climbers. Int J Sport Nutr Exerc Metab. 2019;29(3):259-264. doi:10.1123/ijsnem.2018-0076
10. Płoszczyca K, Czuba M, Zakrzeska A, Gajda R. The effects of six-gram D-aspartic acid supplementation on the testosterone, cortisol, and hematological responses of male boxers subjected to 11 days of nocturnal exposure to normobaric hypoxia. Nutrients. 2024;16(1):76. doi:10.3390/nu16010076
11. Willoughby DS, Spillane M, Schwarz N. Heavy resistance training and supplementation with the alleged testosterone booster NMDA has no effect on body composition, muscle performance, and serum hormones associated with the hypothalamo-pituitary-gonadal axis in resistance-trained males. J Sports Sci Med. 2014;13(1):192-199. PubMed 24570624
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13. GamalEl Din SF, Elkhiat Y, Hussein T, et al. Evaluation of supplementation of 2660 mg D-aspartic acid and 200 mg ubiquinol and 10 mg zinc on different semen parameters in idiopathic male infertility: a randomized double blind placebo controlled study. Arch Ital Urol Androl. 2025;97(2):13554. doi:10.4081/aiua.2025.13554