L-arginine can lower blood pressure, and the effect is meaningful. A meta-analysis of 11 clinical trials found that supplementation reduced systolic blood pressure by about 5.4 mmHg and diastolic by about 2.7 mmHg compared to placebo. That’s a modest but clinically relevant drop, roughly comparable to what some people achieve through dietary changes like reducing sodium.
How L-Arginine Lowers Blood Pressure
Your blood vessels are lined with cells that produce nitric oxide, a molecule that tells the surrounding muscle tissue to relax. L-arginine is the raw material your body uses to make nitric oxide. When you take it as a supplement, your endothelial cells convert it in a two-step chemical reaction: first into an intermediate compound, then into nitric oxide and a byproduct called citrulline.
Once produced, nitric oxide drifts into the smooth muscle cells wrapped around your blood vessels. There it triggers a chain reaction that ultimately lowers calcium levels inside those muscle cells. Less calcium means the muscle relaxes, the vessel widens, and blood flows through with less resistance. That’s the drop in blood pressure. It also inhibits platelet clumping, which helps keep blood flowing smoothly.
What the Clinical Evidence Shows
The most cited meta-analysis, pooling 11 randomized trials with 387 participants, found an average systolic reduction of 5.39 mmHg and diastolic reduction of 2.66 mmHg. Trial durations ranged from 2 to 24 weeks, with daily doses between 4 and 24 grams. A larger dose-response meta-analysis confirmed these findings and added an important detail: doses of 9 grams per day or less actually produced bigger reductions than higher doses. At 9 grams or under, systolic pressure dropped by an average of 9.36 mmHg and diastolic by 4.26 mmHg.
Results can appear quickly. In one study of 29 healthy individuals given L-arginine for just one week, systolic blood pressure dropped in 62% of participants (average decrease of 4 mmHg) and diastolic dropped in 69% of participants (average decrease of 3.7 mmHg). So you don’t necessarily need months to see a change, though longer supplementation may sustain the effect.
Dosage: More Isn’t Better
The effective threshold appears to be at least 4 grams per day for a measurable reduction in systolic blood pressure. But there’s a ceiling. Doses above 9 grams per day failed to significantly lower blood pressure in multiple analyses, and supplementation lasting longer than 24 days didn’t consistently outperform shorter courses. The pattern held for both systolic and diastolic readings.
This inverted dose-response is unusual but well-documented. The most practical range based on current evidence is 4 to 9 grams daily, split across the day. Taking more won’t help and may increase side effects without added benefit.
Side Effects and Safety
At typical supplemental doses of 3 to 6 grams taken at once, side effects are rare. Gastrointestinal symptoms like nausea, bloating, and diarrhea become more common at single doses above 9 grams. The diarrhea is likely related to how L-arginine stimulates nitric oxide production in the gut, which is the same mechanism behind many laxatives. Healthy people tend to be more sensitive to these effects than those with conditions like diabetes.
One serious safety concern: L-arginine should not be taken by anyone who has recently had a heart attack. A randomized clinical trial published in JAMA (the VINTAGE MI trial) found potential harm in post-heart attack patients. The suspected reason is that after a heart attack, the enzyme that normally converts L-arginine into nitric oxide can malfunction, producing damaging reactive oxygen species instead. Additional L-arginine in that scenario may feed the wrong pathway.
Drug Interactions
Because L-arginine lowers blood pressure through its own mechanism, combining it with blood pressure medications can cause an excessive drop. Cleveland Clinic lists several drug classes that interact with L-arginine:
- ACE inhibitors (enalapril, lisinopril, benazepril)
- Beta-blockers (metoprolol, atenolol, carvedilol)
- Calcium channel blockers (amlodipine, diltiazem, nifedipine)
- Angiotensin receptor blockers (losartan, valsartan, candesartan)
- Alpha-blockers (doxazosin, prazosin)
- Nitrates (nitroglycerin, isosorbide)
Nitrates deserve special attention because they also work through nitric oxide pathways. Combining them with L-arginine can amplify the blood pressure drop unpredictably. Fish oil supplements may also interact, since they have their own mild blood-pressure-lowering effects.
L-Arginine During Pregnancy
L-arginine has drawn particular interest for preventing and treating preeclampsia, a dangerous pregnancy complication involving high blood pressure. A systematic review of 19 randomized trials involving nearly 2,000 women found that L-arginine was associated with a 48% reduced risk of developing preeclampsia in prevention trials. For severe preeclampsia, the risk reduction was even larger at 77%. In women already diagnosed, supplementation lowered systolic blood pressure by about 5.6 mmHg on average.
These results are promising enough that the Accelerating Innovations for Mothers project identified L-arginine as one of five high-potential medicines for preeclampsia prevention. However, the certainty of the evidence is still rated low, and the trials varied in size and design. This is not something to self-prescribe during pregnancy.
L-Arginine vs. L-Citrulline
L-citrulline is often marketed as a better alternative because your body converts it into L-arginine, and citrulline bypasses first-pass metabolism in the liver, meaning more of it reaches circulation. Both supplements can acutely lower blood pressure in short-term studies. However, a 2024 review of registered clinical trials concluded that the evidence for either supplement having a reliable chronic blood pressure-lowering effect in the general population is inconsistent. The trial designs vary so widely in dosage, duration, and population that comparing the two head-to-head remains difficult. Neither has a clear advantage over the other based on current data.
Who Benefits Most
The blood pressure reductions seen in trials were strongest in people who already had elevated readings. Subgroup analyses found that L-arginine did not significantly reduce blood pressure in obese individuals (BMI over 30), which may relate to the higher levels of inflammation and oxidative stress that can impair nitric oxide production. People with mild to moderate hypertension and a BMI under 30 appear to be the best candidates based on existing data. The supplement is not a replacement for medication in people with significantly elevated blood pressure, but for those in the borderline range looking for non-pharmaceutical options, the evidence supports a real, if modest, effect.