The Best Nitric Oxide Supplements for ED: Top Picks

Erectile dysfunction (ED) is mostly a blood flow problem, and the molecule at the center of blood flow to the penis is nitric oxide (NO). When NO signaling works, the arteries relax, blood rushes in and an erection follows. When it falters, desire is there but the body doesn’t follow through.

That is why “nitric oxide boosters” are sold for ED. A few of them have real human data behind them, mostly small trials in men with mild to moderate ED. Many others are padded formulas with little evidence.

This guide covers how nitric oxide drives an erection, which supplements have been studied for ED, the doses used in those studies, and who should avoid them.

How Nitric Oxide Drives an Erection

Sexual arousal makes nerve endings and the lining of the blood vessels (the endothelium) in the penis release nitric oxide. NO switches on an enzyme that produces cGMP, a messenger that relaxes the smooth muscle in the arteries and erectile tissue. This process is called vasodilation.

As the erectile tissue fills with blood, it presses on the veins that would normally drain it. That trapping of blood is what keeps an erection firm. If NO signaling is weak, the arteries don’t open fully, less blood gets in, and erections are softer or don’t last.

Prescription ED drugs work on the same pathway. Sildenafil (Viagra) and tadalafil (Cialis) block PDE5, the enzyme that breaks down cGMP. They don’t force an erection; they amplify the signal that NO starts, which is why they still need sexual stimulation. NO supplements take the other route: they try to give the body more raw material to make NO in the first place.

Why Nitric Oxide Levels Drop

NO availability tends to fall with age and is often lower in men with diabetes, obesity, high blood pressure, high cholesterol, heart disease or a smoking habit. All of these damage the endothelium, the same tissue that produces NO. That is why ED often shows up years before other signs of heart disease, and why new ED deserves a medical check-up, not just a supplement.

Low testosterone can play a part too, mainly by lowering libido, but most ED in otherwise healthy men is vascular. Supplements that support NO make the most sense for mild, blood-flow-related ED.

The Best Nitric Oxide Supplements for ED

Below are the ingredients with the most research for ED, ranked by the quality of the human evidence. Doses are those used in studies, not personal advice.

1. L-Citrulline

L-citrulline is an amino acid found in watermelon. It works indirectly: the kidneys convert it into L-arginine, which the body then uses to make NO. Because citrulline avoids the breakdown that arginine suffers in the gut and liver, oral citrulline raises blood arginine levels more reliably than arginine itself.

The evidence: a small single-blind, placebo-controlled study published in Urology in 2011 gave 1.5 g of L-citrulline per day for one month to 24 men with mild ED (average age 56.5). While taking citrulline, 50% of the men improved from mild ED to normal erection hardness, compared with 8.3% while taking placebo. No side effects were reported.

Doses used in studies: 1.5 g per day of L-citrulline in the ED study. Exercise studies usually use 6-8 g of citrulline malate about an hour before training. Citrulline malate is only partly citrulline (roughly 55-70%, depending on the ratio), so check which form a label lists.

2. L-Arginine

L-arginine is the direct building block that nitric oxide synthase turns into NO. It is the most studied NO supplement for ED. The catch is that much of an oral dose is broken down in the gut and liver before it reaches the bloodstream, which is why studies use gram-level doses.

The evidence: a 2019 meta-analysis in the Journal of Sexual Medicine pooled 10 randomized trials (about 540 men) and found that 1.5-5 g of arginine per day improved erectile function scores compared with placebo or no treatment in men with mild to moderate ED. A placebo-controlled trial of long-term, high-dose L-arginine in men with vasculogenic (blood-flow-related) ED also reported better erectile function, with the clearest benefit in mild to moderate cases. Results in severe ED are weak.

Some researchers have also combined daily L-arginine with low-dose tadalafil. A 2020 randomized study using 2.5 g of arginine plus 5 mg of tadalafil a day reported better erectile function scores than either one alone. That combination was used under medical supervision, so don’t add arginine to a prescription ED drug without asking your doctor.

Doses used in studies: roughly 1.5-5 g per day, often split into two or three doses, taken daily for 1-3 months.

3. Pycnogenol + L-Arginine

Pycnogenol is a standardized extract of French maritime pine bark. It is thought to support the enzyme that makes NO (eNOS), while arginine supplies the raw material.

The evidence: a 2003 study in the Journal of Sex & Marital Therapy followed 40 men aged 25-45 with ED. One month of L-arginine alone (1.7 g per day) gave normal erections in 5% of them. After adding 80 mg of Pycnogenol a day in month two, that rose to 80%, and to 92.5% after month three on 120 mg a day. The results are striking, but the study had no placebo group, so treat them as a promising signal rather than proof.

4. Beetroot (Dietary Nitrate)

Beetroot is rich in nitrate, which mouth bacteria convert into nitrite and the body then turns into NO. This route doesn’t depend on arginine at all. Beetroot juice reliably raises nitrite levels and modestly lowers blood pressure in studies, and it is a popular sports supplement. Antibacterial mouthwash blunts the nitrate-to-nitrite step, so it can reduce the effect.

The evidence: there are no good trials of beetroot for ED. A randomized, placebo-controlled trial in trained male triathletes gave 3 g of citrulline plus beetroot extract providing 300 mg of nitrate a day for 9 weeks and found better strength and aerobic power than placebo. That is performance data, not ED data.

5. Grape Seed Extract and Hawthorn Berry

Both have antioxidant properties and some evidence for blood vessel function. Neither has meaningful ED data. They are reasonable extras in a formula, but they shouldn’t be what you are paying for.

Nitric Oxide Supplements for ED Compared

How to Choose a Nitric Oxide Supplement

• Read the label. Look for L-citrulline, L-arginine or standardized Pycnogenol with exact doses. Skip proprietary blends that hide the amounts.
• Compare doses to the studies. A product with 200 mg of arginine is far below the 1.5-5 g used in trials.
• Prefer third-party testing. Independent testing confirms the product contains what the label says.
• Avoid “male enhancement” pills. The FDA has repeatedly found sexual enhancement supplements spiked with hidden sildenafil or tadalafil, which is dangerous for men on nitrate medication.
• Give it time. The ED studies used daily dosing for one to three months. A single dose before sex is not what was tested.

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Pros

• Catalog is specifically organized around muscle building, fat loss, testosterone support, and workout performance.
• Range includes creatine, protein, EAAs, beta-alanine, and L-citrulline alongside more specialized formulas.
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Cons

• Features several strong claims around muscle growth, testosterone, fat loss, and metabolic effects that should be distinguished from independently demonstrated clinical outcomes
• Heavily oriented toward bodybuilding and performance rather than broader nutritional supplementation.

Other Benefits of Better Nitric Oxide Levels

The same mechanism that helps erections affects blood vessels everywhere, so supporting NO can have knock-on effects:

• Blood pressure: dietary nitrate and, in some studies, arginine and citrulline modestly lower blood pressure. This is a small effect, not a replacement for medication.
• Training: citrulline malate is a common pre-workout ingredient for the pump, and some studies report more reps and less soreness. Results across studies are mixed.
• Endurance: beetroot nitrate can lower the oxygen cost of exercise, with the clearest effects in recreational rather than elite athletes.

Confidence often improves when erections become reliable again, but that is a result of better function, not a separate effect of the supplement.

Side Effects of Nitric Oxide Supplements

At the doses used in studies, these supplements are usually well tolerated. Side effects that do occur include:

• Stomach upset: bloating, cramps, nausea or diarrhea, mostly with large single doses of arginine. Splitting the dose and taking it with food helps.
• Headache and flushing: from wider blood vessels, more likely when combined with other vasodilators or stimulant pre-workouts.
• Low blood pressure: L-arginine and nitrate can lower blood pressure, which may cause dizziness when you stand up, especially if you already take blood pressure medication.
• Beeturia: beetroot can turn urine or stool pink or red. It is harmless.

Who Should Avoid Nitric Oxide Boosters

• Men taking nitrate medication such as nitroglycerin for chest pain. Nitrates combined with PDE5 inhibitors can cause a dangerous drop in blood pressure, and NO supplements add to the same effect. Don’t combine anything without your doctor.
• Men on PDE5 inhibitors or blood pressure drugs, unless a doctor approves. The effects can add up.
• Anyone who has had a heart attack. In a 2006 trial in heart attack survivors, L-arginine did not improve blood vessel stiffness and was stopped early after more deaths in the arginine group than with placebo.
• People with low blood pressure, kidney or liver disease, or anyone with an upcoming surgery. Tell your surgeon about every supplement you take; many ask patients to stop supplements about two weeks beforehand.
• Under-18s. ED in young men is uncommon and should be checked by a doctor rather than self-treated.

Stacking Nitric Oxide Supplements

ED usually has more than one cause, so some men pair an NO supplement with something that targets another factor. The evidence for these combinations is thinner than for the single ingredients above.

NO + Testosterone Support

For men with low libido as well as ED. NO handles blood flow, while testosterone boosters such as tongkat ali or fenugreek have small studies on libido. If you suspect low testosterone, a blood test tells you more than any supplement.

NO + Adaptogens

Stress and performance anxiety are common causes of ED. Ashwagandha has some evidence for lowering stress and cortisol. Pairing it with an NO supplement covers both the mental and the vascular side.

NO + Creatine or Pre-Workout

For lifters. Citrulline already sits in many pre-workouts, and creatine supports strength and power. Count the total citrulline across products so you don’t double up.

Timing and Dosing

• For ED, the studies used daily dosing over weeks, not a single dose before sex.
• For training, citrulline malate is usually taken about an hour before the session.
• Split larger arginine doses and take them with food if your stomach complains.
• There is no evidence that you need to cycle these supplements on and off.
• Avoid stacking several vasodilators at once unless a doctor is monitoring you.

If supplements don’t help after a few months, proven treatments exist, from PDE5 inhibitors to options covered in our guide to peptides for erectile dysfunction.