Taking 6 grams of L-arginine might help healthy young men lower their blood pressure and increase a chemical in their blood that helps blood vessels relax.

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.

Taking a specific amount of arginine supplement for just three days doesn’t change the levels of nitric oxide in the blood of highly trained male athletes when they do short, intense workouts.

Taking L-arginine pills every day for a few weeks to a few months might help lower your blood pressure a little—like how eating healthier foods (such as the DASH diet) does.

Taking a 5-gram dose of L-arginine won’t help healthy young men cycle better or lower ammonia in their blood, even though it does raise levels of a few other related chemicals in their blood.

Taking a specific supplement called L-citrulline every day for a week, plus a little more before working out, can boost a key chemical in your blood by about three-quarters — and that chemical helps your body make nitric oxide, which is good for blood flow.