A1
L-citrulline
- Product declaration
- L-Citrulline: 6000 mg
- Selected studied range
- 3000 to 9000 mg
- Protocol and duration
- per day, in the studies NIH ODS summarizes
- Studied context
- Studied as a nitric-oxide pathway precursor (converted to arginine via the urea cycle) for aerobic exercise performance measures such as oxygen-uptake (VO2) kinetics, blood lactate, and rate of perceived exertion, and for acute resistance-exercise performance and muscle oxygenation. NIH ODS describes evidence for enhancing performance as limited, with few studies and conflicting results.
- Limitations
- A 2022 systematic review/meta-analysis found no significant benefit for endurance-performance outcomes specifically. A single 8 g acute dose did not enhance isometric force production, muscle endurance, or muscle-oxygenation parameters in one resistance-exercise study. NIH ODS characterizes overall performance-enhancement evidence as limited.
Selected evidence: NIH ODS, Dietary Supplements for Exercise and Athletic Performance · Open source
A2
Beta-alanine
- Product declaration
- Beta-Alanine: 1200 mg
- Selected studied range
- 4000 to 6000 mg
- Protocol and duration
- per day in divided doses, for at least 2 to 4 weeks, not as a single pre-workout dose
- Studied context
- Studied for high-intensity exercise capacity in the 60-240 second range via elevation of muscle carnosine, which acts as an intracellular pH buffer against acidosis. ISSN 2015 position stand: greatest performance benefits in "open end-point" tasks/time trials lasting 1-4 minutes; some benefit noted in aerobic exercise up to roughly 25 minutes; attenuation of neuromuscular fatigue, particularly noted in older adults.
- Limitations
- Strength/resistance-training outcomes remain mixed; training volume may increase without a clear strength gain. Tasks under 60 seconds do not show benefit. Endurance benefit beyond about 25 minutes is not established. Long-term safety data beyond roughly a year, and effects in special/tactical populations, are flagged as needing more research.
Selected evidence: ISSN position stand on beta-alanine, 2015 · Open source
A2
Taurine
- Product declaration
- Taurine: 1200 mg
- Selected studied range
- 1000 to 3000 mg
- Protocol and duration
- per day, acutely across 6 to 15 days
- Studied context
- Studied for aerobic performance (VO2max, time-to-exhaustion, time-trial performance), anaerobic/strength performance, exercise-induced muscle damage, and recovery. A 2018 review ("Taurine in sports and exercise," PMC8152067) reports small-to-moderate improvements across several of these outcomes in some studies.
- Limitations
- The 2018 review states plainly: "limited and varied findings prohibit definitive conclusions regarding the efficacy of taurine on aerobic and anaerobic performance," and separately notes no peer-reviewed evidence exists for an independent role of taurine in skeletal-muscle hypertrophy.
Selected evidence: Taurine in sports and exercise, 2018 · Open source
A2
Alpha-GPC
- Product declaration
- AlphaSize® (Alpha-GPC): 100 mg
- Selected studied range
- 300 to 600 mg
- Protocol and duration
- single dose, 30 to 90 minutes before testing or training
- Studied context
- Studied for acute cognitive performance (e.g., Stroop-test measures) and for acute power output/strength in resistance exercise. A 2024 study found both 300 mg and 600 mg doses improved Stroop-test performance in healthy young men. Separate studies cited 600 mg dosed 90 minutes pre-exercise increasing post-exercise growth hormone and peak bench-press force, and 600 mg/day over 6 days increasing lower-body isometric strength by over 3%.
- Limitations
- NIH ODS's Choline Health Professional fact sheet does not mention alpha-GPC at all, and states no studies have compared relative bioavailability across the choline supplement forms it does cover (choline bitartrate, phosphatidylcholine, lecithin). Alpha-GPC's comparative bioavailability is outside what NIH has assessed in that document. A large 2021 observational study (JAMA Network Open, South Korean national-insurance cohort, n=12,008,977 adults 50+) found an association between alpha-GPC use and 10-year stroke risk (adjusted HR 1.46, 95% CI 1.43-1.48 for total stroke) in a dose- and duration-response pattern, but the authors explicitly flag confounding limitations: alpha-GPC users were older with more comorbidities at baseline, and the study is observational (association, not proven causation).
Selected evidence: Acute alpha-GPC supplementation and cognitive performance, 2024
A4
Huperzine A
- Product declaration
- Huperzine A: 250 mcg
- Selected studied range
- No dose range selected
- Protocol and duration
- Not recorded in the selected comparison
- Studied context
- Marketed for memory, alertness, attention, concentration, and focus, and studied preliminarily in Alzheimer's disease populations (it is used as an approved pharmaceutical for this purpose in China). The DoD's Operation Supplement Safety (OPSS) resource, reviewing the evidence base, states plainly: "No reliable scientific evidence supports the use of huperzine A to enhance cognitive performance" in healthy individuals specifically.
- Limitations
- OPSS states no reliable evidence supports cognitive-enhancement use in healthy people; the Alzheimer's Association explicitly recommends against use, especially combined with prescription drugs, citing insufficient safety data and poorly understood long-term effects.
Selected evidence: Operation Supplement Safety, huperzine A · Open source
