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 daily L-arginine supplement for two weeks doesn't help lower ammonia levels in the blood when healthy young men cycle hard, because the supplement group and the placebo group ended up with pretty much the same ammonia levels.

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 daily L-arginine supplement for two weeks doesn't make healthy young men cycle any harder or faster in a short, self-paced test compared to taking a sugar pill.

Taking L-arginine pills in these amounts doesn’t raise the levels of L-arginine or related molecules in your blood or urine, because your body breaks them down too quickly before they can get into your system.

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.