A sports supplement improved fatigue a little
STUDY: Kang EB et al, Nutrients 2026
STUDY TYPE: Randomized controlled trial
FUNDING: ARI BnC Co., Ltd.; product supplied by Daesang Wellife Co., Ltd.
Background
L-arginine is an amino acid that the body converts to nitric oxide, which widens blood vessels. In theory, it improves fatigue by enhancing blood flow, helping muscles clear lactate and recover.
The Study
- 120 Korean adults ages 30 to 59 with persistent fatigue but no major illness; 79% were women. 119 were analyzed.
- Randomized to L-arginine 3 g/day, 6 g/day, or placebo for 8 weeks.
- Primary outcome: Fatigue scale (FSS, scored 9 to 63). Secondary outcomes included a Sleep scale (PSQI) and blood lactate after a 30-minute treadmill run.
Results
Fatigue scores fell 6.4 points on 6 g/day and 2.2 points on placebo, a difference of about 4 points. The 3 g/day dose did no better than placebo.
The 6 g/day group still averaged above the fatigue cutoff used for enrollment.
Sleep improved slightly at both doses, an exploratory finding. Lactate after exercise was lower on 6 g/day, but nitric oxide levels didn’t change.
Side Effects and Risks
- No serious adverse events in this trial, though one case of heartburn and one of palpitations in the high-dose group
- Avoid l-arginine patients with recent myocardial infarction (worsens mortality rates). Avoid in melanoma or hepatocellular cancer (it may increase tumor growth but does not cause cancer). Anticoagulant (a theoretical risk; hold two weeks before surgery). May raise potassium in patients with renal or hepatic impairment.
Limitations
- Industry-funded and registered after the study ended.
- Single site, small, and mostly women.
- Several statistical adjustments were made after the fact.
Practice Implications
- Small difference, only the higher dose worked, and statistical manipulations… let’s wait for confirmation.
- L-arginine has better evidence for erectile dysfunction, where it worked on its own or augmented Viagra-like drugs in large, randomized trials. Learn how to use it in The Complementary and Alternative Medicine in Psychiatry Fact Book.
- When treating fatigue, first look common causes: depression, sleep apnea, thyroid disease, anemia, and medication side effects (including SSRIs, which disrupt sleep quality in 16%).
—Chris Aiken, MD
Director, Psych Partners
Editor in Chief, Carlat Psychiatry Report
