Arginine

Reasonable evidence for blood-pressure reduction and mild exercise-performance effects. Citrulline may be a more effective NO precursor due to better oral bioavailability.

A rough internal score reflecting quantity, quality, and consistency of human evidence. Not a clinical recommendation.

Meta-analyses support a small but consistent blood-pressure-lowering effect (2–5 mmHg systolic). Exercise studies show mixed results for performance. Oral bioavailability is limited by extensive first-pass metabolism. Citrulline raises plasma arginine more effectively.

• Modest blood-pressure reduction in meta-analyses
• Substrate for nitric oxide production
• May improve erectile function in mild cases

3–6 g/day in divided doses. Higher doses may cause GI distress.

• GI discomfort at high doses
• Bloating
• Diarrhea

Avoid in active herpes outbreaks (theoretical concern of promoting viral replication). May interact with blood-pressure and nitrate medications.

Oral absorption is suboptimal. Citrulline often achieves higher plasma arginine levels than arginine itself.

• Recovery35
• Libido35
• Muscle30