Positives

• Long COVID patients on L-arginine 1.66 g + liposomal vitamin C 500 mg twice daily for 28 days commonly report dramatic fatigue resolution (only 8.7% still had fatigue at follow-up versus 80.1% on placebo), with handgrip strength and 6-minute walk distance also improving MDPI Nutrients.
• L-arginine averages 8.5/10 on Drugs.com with 83% reporting positive results — one patient with cardiac history said leg pain resolved within a month and running endurance returned, and a hypertensive patient said their blood pressure normalized without medication Drugs.com.

Negatives

• The benefit appears to depend on co-administration with vitamin C; l-arginine alone has not been studied head-to-head in Long COVID, and uncoupled endothelial NO synthase can theoretically generate harmful peroxynitrite if substrate is given without antioxidant support RTHM.
  
  

Hurdles & Side Effects

• Common side effects at the trial dose (1.66 g l-arginine + 0.5 g vitamin C twice daily) were mild GI upset and headache; high-dose l-arginine can lower blood pressure, which is relevant for Long COVID patients with overlapping low BP or POTS PubMed.
  
  
• Patients with active herpes infections should be cautious because arginine can promote viral replication; l-citrulline (which the body converts to arginine more efficiently) is sometimes preferred when herpes is a concern Nutrients.