Animal studies show that neither oral nor intravenous delivery of arginine causes toxicity, even at high doses.[1][2] However, supplementation with arginine has been reported to cause adverse gastrointestinal effects in humans, including nausea, vomiting, and diarrhea.[3] For this reason, upper-limit guidelines of approximately 20 to 30 grams per day have been proposed for supplemental arginine intake,[4][5] but more long-term safety data in humans are needed to accurately define a tolerable upper intake level.