L-arginine is an amino acid studied for possible effects on blood pressure and other health outcomes. Human studies are small to moderate in size. They show a modest blood pressure drop in a handful of trials and possible benefit in pregnancy-related high blood pressure. They show no benefit for infections in critically ill patients, and the evidence for wound healing is inconclusive. None of the studies summarized below tested it for erectile dysfunction, penis size, or against Viagra.
Quick facts
| Item | What the studies show |
|---|---|
| Forms studied | Oral L-arginine; arginine added to tube or oral nutrition formulas for critically ill patients; L-arginine given during heart surgery; L-citrulline (a precursor the body converts toward arginine) in one related trial |
| Doses used | The study summaries do not list L-arginine doses. The only dose given is for L-citrulline, 3 g twice daily, in one trial (see the dose section) |
| Typical study length | Wound studies ran 2 to 20 weeks; the citrulline trial ran 12 weeks. Other reviews do not state durations |
| Main studied uses | Blood pressure, pre-eclampsia, heart bypass surgery markers, critical illness, pressure ulcers |
What happens if you take L-arginine daily?
The best-studied daily effect is a small drop in blood pressure, covered below. The reviews summarized here do not describe long-term daily use in healthy people, so what happens over months or years is not answered by these studies. If you take blood pressure or heart medicines, ask your pharmacist or clinician before adding any amino acid supplement.
What do human studies show, use by use?
Blood pressure: small drop, few trials
A 2026 meta-analysis in Nitric Oxide pooled 5 randomized trials with 202 participants that measured blood pressure over 24 hours. Oral L-arginine lowered 24-hour systolic pressure by about 4.2 mmHg and diastolic by about 3.0 mmHg compared with control. Night-time drops were slightly larger (about 5.7 and 4.2 mmHg). The authors say the number of trials was limited and more research is needed. With only five trials, treat this as a promising but unsettled result. Our guide to meta-analyses and systematic reviews explains why pooled numbers from few small trials deserve caution.
Pre-eclampsia: possible signal, low certainty
A 2025 systematic review in BJOG covered 20 randomized trials (2,028 women) and 3 non-randomized trials. In prevention trials, L-arginine was linked to a lower risk of pre-eclampsia (relative risk 0.52, four trials) and severe pre-eclampsia (relative risk 0.23, three trials), both rated low-certainty. In treatment trials it may have lowered systolic pressure by about 5.6 mmHg (very low certainty) and fetal growth restriction (low certainty). Eight of the 20 randomized trials had a high risk of bias. The authors call it promising but say results must be read cautiously and that the best dose and timing are still unknown. Pregnancy decisions belong with an obstetric clinician.
Critical illness: no benefit found
A 2026 review in JPEN pooled 23 randomized studies (2,311 patients) of arginine-enriched nutrition in intensive care. It did not reduce infections (relative risk 0.98, 95% CI 0.63 to 1.54) or other outcomes. Certainty was mostly low and results varied widely. None of the studies tested arginine alone, since it was added to formulas with other ingredients.
Heart bypass surgery: changes in lab markers
A 2024 review in BMC Cardiovascular Disorders pooled 7 randomized trials of L-arginine (as a supplement or an infusion during cardioplegia) in people having coronary bypass surgery. Troponin T (a heart-injury marker) and interleukin-6 (an inflammation marker) were lower with L-arginine. CPK-MB, TNF-alpha and troponin I did not change meaningfully. These are lab markers, not proof people did better or lived longer; see our explainer on surrogate outcomes.
Pressure ulcers: inconclusive
A 2025 review in Wound Repair and Regeneration covered 15 studies (1,085 adults). Arginine or arginine plus glutamine showed a trend toward better healing, with wound size reductions from 18.6% to 98.2% over 2 to 20 weeks. But seven studies found non-significant or unreported differences in wound size, and six had the same problem for healing time. Glutamine was only tested alongside arginine. The authors conclude the evidence is inconclusive.
A related trial: L-citrulline in leg artery disease
This one tested L-citrulline, not L-arginine. A phase II crossover trial in 51 people with peripheral artery disease, posted in abstract form on LinkedIn from JACC: Advances (2025), gave 3 g of L-citrulline twice daily for 12 weeks. Blood arginine rose from 75.2 to 119.2 µmol/l. Walking distance improved 20.1% versus 5.7% with placebo. The authors call it a pilot needing confirmation. It shows citrulline can raise arginine levels, not that arginine pills do the same thing.
Is L-arginine better than Viagra, and what about erectile dysfunction?
No study summarized on this page tests L-arginine for erectile dysfunction, penis size, or against Viagra (sildenafil), so there is no basis here to say which works better. Claims of something “10 times more potent than Viagra,” a “new pill to replace Viagra,” or a traditional remedy that works “without Viagra” are not supported by any study listed here. The studies summarized here do not address the causes or treatment of erectile problems. Our guide to ingredient evidence versus marketing claims helps you test such claims.
How quickly does it work?
The reviews here do not report onset times for L-arginine. Wound trials lasted 2 to 20 weeks, and the citrulline trial ran 12 weeks before its walking-distance result. Nothing here shows a same-day or same-week effect.
Doses used in studies
This is what researchers used, not a recommendation. The summaries above do not state the L-arginine amounts used in the blood pressure, pregnancy, surgery, critical illness or wound studies. The BJOG authors say the best dose and start time for pre-eclampsia are still undetermined. The one dose in the pack is 3 g of L-citrulline twice daily for 12 weeks. The captured study summaries do not provide the L-arginine doses.
Safety, side effects and interactions: what is the dark side?
The summaries here give no list of side effects, official warnings or medicine interactions for L-arginine. The critical illness review tracked adverse events, but its summary reports no benefit, not a safety finding. Because blood pressure dropped in trials, it is reasonable to ask a pharmacist or clinician about taking L-arginine alongside blood pressure medicines. Check the full safety information on your product label and with a clinician rather than relying on a marketing page. For general safety and regulatory information on supplements and medicines, the U.S. FDA website is an official place to look.
Who should talk to a clinician first?
- Anyone taking prescription medicines, especially for blood pressure, heart disease or erectile dysfunction.
- Anyone who is pregnant or planning pregnancy. The pre-eclampsia studies were trials in a clinical setting.
- Anyone with heart disease, recent heart surgery, a serious illness or a pressure ulcer.
L-arginine should not be treated as a replacement for a prescribed medicine, and none of the studies above were designed to test that. A clinician is the right person to decide about changes to any medicine.
What is still unknown?
- Blood pressure: only 5 trials, 202 people, so the size and durability of the drop are uncertain.
- Pre-eclampsia: results are low or very low certainty, and the ideal dose and timing are unsettled.
- Critical illness and wounds: no clear benefit, and arginine was mostly tested inside mixed formulas.
- Erectile function, body size and long-term daily use: not covered by these studies.
How to read a label that lists L-arginine
- Look for the amount per serving in grams or milligrams, and compare it with the amount used in the study behind any claim.
- Check the form. L-arginine and L-citrulline are different ingredients, and the one positive walking trial used citrulline.
- Be wary of a “proprietary blend” that lists a total weight but not each ingredient’s amount, since you cannot tell how much L-arginine you get.
- Note whether it is combined with other ingredients; the nutrition-formula studies could not isolate arginine’s effect.
Before you order
- Does the label state the exact L-arginine amount per serving?
- Does the maker point to a human study using that form and amount?
- Have you asked a pharmacist about interactions with your medicines?
By ClinicalStudyConnect.com Research Desk
This article is for general information purposes only and does not constitute medical advice. Consult your doctor or qualified healthcare provider before making changes to your health routine.