Quick answer
NIH says the most commonly reported side effects of arginine at 9 to 30 g a day are stomach and gut discomfort, such as diarrhea and nausea. A review found single doses of 3 to 6 g rarely caused side effects, and most gut effects came with single doses above 9 g. Ask your doctor if you have kidney disease.1,2
Key facts
- NIH says that at 9 to 30 g a day the most commonly reported side effects of arginine are gut discomfort, such as diarrhea and nausea, and slightly lower blood pressure.1
- A review of clinical trials found single doses of 3 to 6 g rarely caused side effects.2
- In that review, most nausea, vomiting and diarrhea came with single doses above 9 g, often within a daily total near 30 g or more.2
- The effects seemed to depend on how the amount was taken, and they disappeared when it was divided into smaller doses.2
- A 2016 systematic review concluded that short-term arginine use may cause stomach and gut effects, and effects on the heart and circulation.3
What does NIH say about arginine and diarrhea?
NIH's Office of Dietary Supplements puts diarrhea on the short list of arginine's side effects. In its fact sheet for health professionals, the most commonly reported adverse reactions at 9 to 30 g a day are gastrointestinal discomfort such as diarrhea and nausea, and slightly lower blood pressure. The same sheet says most study results suggest that up to 9 g a day for several days or weeks was well tolerated.1
At 9 to 30 g a day, the most commonly reported side effects are stomach and gut discomfort, such as diarrhea and nausea.1,4
A 2016 systematic review of 62 studies in healthy adults aged 19 to 50 reached a compatible conclusion: short-term supplementation may cause gastrointestinal effects as well as effects on the heart and circulation.3
How much arginine does it take?
A 2007 review in the Journal of Nutrition looked at the clinical trials of arginine and related amino acids, with intakes from 3 g a day to over 100 g a day. It noted that the standard of reporting adverse effects varied.2
| Amount | What the review reported |
|---|---|
| Single doses of 3 to 6 g | Rarely caused side effects |
| Single doses above 9 g (more than about 140 mg per kg of body weight) | Most of the nausea, vomiting and diarrhea occurred at this size |
| Daily totals near 30 g or more | Often the pattern when single doses above 9 g caused trouble |
| The same total divided into smaller doses | Effects disappeared |
These figures describe where effects were seen in trials, not an amount to aim for. They also come from a review of mixed studies, and the author said more research is needed to refine dosing strategies.2
Why would an amino acid cause diarrhea?
The review offers a mechanism. Taken by mouth, arginine is absorbed by a transport system in the small intestine that works well at low levels but can handle only so much at once. Large single doses of a poorly absorbed amino acid seem to provoke diarrhea, and the author linked this to nitric oxide, which at high levels in the gut acts as a secretagogue, meaning it draws water and salts into the intestine. The action of many laxatives is mediated in a similar way.2
The review also noted that healthy athletes seemed more prone than diabetic patients to gut symptoms at single doses above 9 g, and suggested that disease may alter gut motility and absorption. That was the review author's reading across different trials, not a head-to-head comparison.2
What is not known?
The sources do not say how long diarrhea lasts once it starts, apart from the review's observation that effects disappeared when the amount was divided. They also give no figure for how many people get diarrhea at a given amount, because the trials reported side effects unevenly.2
They also do not cover every person. NIH's sheets draw on studies that were small and mostly in young men, so how often women or older adults get diarrhea is not described.1
Who should ask a doctor?
- Anyone with kidney disease should ask before using arginine, because the injection's label asks doctors to consider the nitrogen load arginine adds when kidney function is reduced.5
- Anyone who has recently had a heart attack should ask a doctor first, because in a 2006 trial more people died on arginine than on placebo.6
- Anyone on blood pressure medicine should ask, since NIH says arginine can lower blood pressure.1
- Anyone with severe or lasting diarrhea should tell a doctor, whatever the cause.
Questions people ask
Why does L-arginine cause diarrhea?
A 2007 review linked it to large single doses of a poorly absorbed amino acid, with nitric oxide in the gut drawing water and salts into the intestine. The effect seemed to depend on the dosing pattern.2
How much L-arginine causes diarrhea?
Most gut effects came with single doses above 9 g, often within a daily total near 30 g or more, while single doses of 3 to 6 g rarely caused problems. Those are trial findings, not advice.2
Does L-arginine cause constipation or headaches?
The NIH sheets and reviews we read name diarrhea, nausea and lower blood pressure, and do not name constipation or headaches. That is not a finding either way.1,3
Does L-arginine cause cold sores or herpes outbreaks?
The NIH sheets and reviews we read do not list cold sores or herpes outbreaks among arginine's effects. That is not a finding either way. Ask your doctor if you get them.1,3
Does L-arginine cause gout, liver damage or frequent urination?
None of the sources we read report those effects. The injection's label does ask doctors to consider arginine's nitrogen load when kidney function is reduced. Ask your doctor.5
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Sources
- National Institutes of Health, Office of Dietary Supplements. Dietary Supplements for Exercise and Athletic Performance: Fact Sheet for Health Professionals. Updated April 1, 2024. Opened 2026-10-07.
- Grimble GK. Adverse gastrointestinal effects of arginine and related amino acids. J Nutr. 2007;137(6 Suppl 2):1693S-1701S. Opened 2026-10-07.
- Brooks JR, et al. Safety and performance benefits of arginine supplements for military personnel: a systematic review. Nutr Rev. 2016;74(11):708-721. Opened 2026-10-07.
- National Institutes of Health, Office of Dietary Supplements. Dietary Supplements for Exercise and Athletic Performance: Fact Sheet for Consumers. Updated March 22, 2021. Opened 2026-10-07.
- R-Gene 10 (arginine hydrochloride injection): prescribing information (Pharmacia & Upjohn, Pfizer). DailyMed, U.S. National Library of Medicine. Published April 3, 2024. Opened 2026-10-07.
- Schulman SP, et al. L-arginine therapy in acute myocardial infarction: the Vascular Interaction With Age in Myocardial Infarction (VINTAGE MI) randomized clinical trial. JAMA. 2006;295(1):58-64. Opened 2026-10-07.
This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.