Most people supplement with 3 to 6 grams of L-arginine per day, split into two or three doses. The effective range depends on what you’re taking it for, with study doses ranging from as low as 2.5 grams up to 20 grams daily. The observed safe level for oral supplementation is around 20 grams per day, though most uses call for far less.
General Dosage Range
The Cleveland Clinic puts the average supplemental dose between 6 and 30 grams per day, with most people falling toward the lower end of that range. Splitting your total daily amount into two or three smaller doses improves tolerability and keeps levels steadier in your bloodstream. Taking it on an empty stomach appears to improve absorption, so 30 minutes before meals is a common approach.
Your body also gets L-arginine from protein-rich foods like meat, poultry, fish, dairy, nuts, and seeds. A typical diet provides roughly 4 to 5 grams per day, so supplemental doses add to what you’re already consuming.
Doses Used for Blood Pressure
A large meta-analysis of 22 clinical trials found that L-arginine supplementation lowered systolic blood pressure by an average of 6.4 mmHg and diastolic by 2.6 mmHg. The effective threshold was 4 grams per day or more for systolic improvements, regardless of how long people took it. Interestingly, doses above 9 grams per day did not produce additional benefits, suggesting a ceiling effect. Higher doses also failed to help in obese individuals.
If blood pressure is your goal, the sweet spot appears to be somewhere between 4 and 9 grams daily, divided into smaller doses.
Doses Studied for Erectile Dysfunction
L-arginine works by boosting nitric oxide production, which relaxes blood vessels and increases blood flow. For erectile dysfunction, clinical trials have typically used 2,500 to 5,000 milligrams (2.5 to 5 grams) per day. One multicenter study tested 2,500 milligrams daily for 12 weeks, both alone and combined with a low-dose prescription medication, and found improvements in both groups. Most ED studies run for at least 4 to 12 weeks before measuring results, so this isn’t something that works after a single dose.
Doses for Exercise Performance
Studies on exercise performance have used anywhere from 2 to 6 grams, taken either as a single pre-workout dose or daily for several weeks. The results, however, are underwhelming. A review from the Gatorade Sports Science Institute concluded that L-arginine has not been convincingly shown to increase nitric oxide production during exercise or to improve aerobic performance in either recreational or well-trained athletes.
A few studies did find modest benefits, but they combined L-arginine with other ingredients like citrulline, antioxidants, or grape seed extract, making it hard to credit arginine alone. One study found that 6 grams daily for two weeks improved how quickly the body ramped up oxygen use at the start of moderate cycling, but this didn’t translate into better endurance. If you’re taking it for workouts, 3 to 6 grams about 60 minutes before exercise is the most commonly tested protocol, but don’t expect dramatic results.
Side Effects and the GI Threshold
The most common side effects are gastrointestinal: nausea, bloating, cramping, and diarrhea. How much triggers these symptoms depends largely on how you take it. Single doses of 3 to 6 grams rarely cause problems. Once you push past 9 grams in a single sitting, GI distress becomes much more likely, especially in otherwise healthy people. Interestingly, research has found that diabetic patients tend to tolerate higher doses better than healthy athletes.
Splitting your daily intake into smaller doses is the simplest fix. Side effects that show up with a large single dose often disappear when the same total amount is spread across the day. The diarrhea that high doses cause appears to be driven by nitric oxide activity in the gut, the same mechanism behind many over-the-counter laxatives.
Upper Limits and Safety Concerns
The observed safe level is approximately 20 grams per day for oral use. Short-term studies have tested higher amounts without serious harm, but the long-term safety of very high doses hasn’t been thoroughly established.
One important caution: a trial giving 9 grams daily to patients recovering from a heart attack was stopped early after the supplementation group experienced more deaths and hospitalizations than the placebo group. The exact mechanism isn’t clear, but it prompted a straightforward recommendation from Harvard Health: people with existing heart disease should avoid L-arginine supplements.
Who Should Be Cautious
L-arginine can lower blood pressure on its own, so combining it with blood pressure medications may cause levels to drop too low. If you take blood thinners, it may increase bleeding risk. People on ACE inhibitors face a specific concern: L-arginine can cause potassium levels to rise, which is the same side effect ACE inhibitors already carry, and stacking both raises the risk.
For most healthy adults looking for a starting point, 3 to 6 grams per day in divided doses is well-tolerated and falls within the range used in most clinical research. Staying below 9 grams in any single dose keeps GI side effects low, and there’s limited evidence that going above 9 grams total offers additional benefit for most purposes.