Even when there's already plenty of L-arginine in the blood, adding more still makes more nitric oxide—which is weird because you'd think the body would stop making more once it has enough. This suggests something else besides just having more原料 is controlling how much nitric oxide gets made.

Taking L-arginine or L-citrulline supplements might help lower blood pressure by helping blood vessels relax better, but other things in the body can get in the way and make it less effective.

Taking L-arginine pills can raise the level of arginine in your blood, but that doesn’t always mean you’ll produce more nitric oxide or get better at exercising—sometimes it helps, sometimes it doesn’t.