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 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 a specific amino acid supplement called L-arginine every day for three weeks helps people who’ve had a heart attack and are in rehab walk farther in six minutes than those who take a sugar pill.

Taking arginine supplements for just three days won’t make you stronger or more powerful during short, intense workouts like sprinting or lifting heavy weights—even if you’re already a well-trained athlete.

Taking a specific amino acid supplement called L-arginine every day for three weeks might make people feel less tired when they exercise, after having a heart attack and while doing heart rehab — compared to taking a sugar pill.

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.