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Ingredient guide

Is L-arginine safe? Side effects and who should ask first

Written by the Full Measure editorial team, which sells supplements. Approved for publication by the Full Measure owners. Updated .

Drafted with AI assistance from the sources listed below. How we write these

Quick answer

For healthy adults, NIH says up to 9 g of L-arginine a day for days or weeks is safe and well tolerated in most studies. Higher amounts, 9 to 30 g a day, most often cause stomach discomfort, and the safety of high doses beyond 3 months is unknown. Some people should avoid it or ask a doctor first.1

Key facts

  • No official upper limit is set for arginine.1
  • A 2016 review of 62 studies in healthy adults judged most of them small and prone to bias.2
  • The arginine injection used in hospital tests is a different product: 30 g given into a vein over 30 minutes.3
  • The safety of high-dose arginine taken for more than 3 months is not known.1

The most common side effects

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 concluded that short-term arginine use may cause stomach and gut effects, and effects on the heart and circulation.2

Stomach effects track the amount. NIH describes up to 9 g a day as well tolerated for days or weeks, and the complaints mostly come at 9 to 30 g a day.1

Blood pressure

Arginine can lower blood pressure. NIH notes a slight drop at 9 to 30 g a day, and a 2022 pooled analysis of 22 trials found systolic pressure about 6.4 mmHg and diastolic pressure about 2.6 mmHg lower than with placebo, with the systolic drop seen from about 4 g a day.1,5

That drop is the reason to ask your doctor first if you already take medicine to lower blood pressure, or if your blood pressure tends to run low.5

After a heart attack

In a 2006 trial, 153 people who had just had a first heart attack took 3 g of arginine three times a day or a placebo for 6 months, alongside standard care. Arginine did not change the heart and blood vessel measures studied, 6 people taking it died against none on placebo, and the safety committee stopped enrollment.6

The researchers concluded that arginine should not be recommended after a heart attack. If you have any heart condition, talk to your cardiologist before taking it.6

Kidneys

The label of the arginine injection used in hospitals asks doctors to consider the nitrogen load arginine adds in people with reduced kidney function.3

That caution comes from the label of a large dose given into a vein, not from studies of capsules. It is still a reason to ask your doctor first if your kidneys do not work well.3

Long-term use, pregnancy and children

The safety of high-dose arginine taken for more than 3 months is not known.1

Most of the studies were small and mainly in men aged 18 to 25: only four of the 54 studies in one review included women.1

Pregnancy, breastfeeding and childhood are outside what those studies covered, so ask a doctor first in each case.1

Medicines

The official sources we checked, including NIH's fact sheets, LiverTox, DailyMed labels and MedlinePlus, do not name a specific medicine that interacts with arginine. That is not proof of safety. Because arginine can lower blood pressure, ask your pharmacist before combining it with blood pressure or heart medicines.1,5

What's in ours

What’s in ours

Ashwagandha Complex has 300 mg of L-arginine per serving, a small fraction of the amounts in the studies above. Its other ingredients carry their own cautions, which its product page sets out.1

Questions people ask

Is L-arginine safe for the kidneys?

The sources we use report no kidney problems from arginine taken by mouth, but the label of the hospital injection asks doctors to consider the extra nitrogen load in people with reduced kidney function. If you have kidney disease, ask your doctor first.1,3

Can L-arginine cause stomach problems?

Yes, mainly at higher amounts. Stomach discomfort, nausea and diarrhea are the side effects NIH reports most often, at 9 to 30 g a day.1

Is L-arginine safe for women?

There is little research to go on: only four of the 54 studies in one review included women. Ask your doctor first if you are pregnant or nursing.1

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Sources

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. Shiraseb F, Asbaghi O, Bagheri R, Wong A, Figueroa A, Mirzaei K. Effect of l-Arginine Supplementation on Blood Pressure in Adults: A Systematic Review and Dose-Response Meta-analysis of Randomized Clinical Trials. Adv Nutr. 2022;13(4):1226-1242. Opened 2026-10-07.
  6. 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.