Do nitric oxide supplements work? What the research says

Nitric oxide (or NO for short) is a substance produced naturally by your body. It acts as a vasodilator, which means it widens your blood vessels, improving blood flow and reducing blood pressure. 

Nitric oxide supplements don’t actually contain nitric oxide. Instead, they contain substances like L-citrulline and L-arginine, which are purported to increase nitric oxide production in the body. Some people swear by them, claiming they enhance sexual and athletic performance. But what does the research say? Let’s explore. 

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Nitric oxide supplements typically contain some combination of two amino acids, which are also found naturally in our bodies and play a role in nitric oxide production (Bescos, 2012). 

• L-arginine: This essential amino acid (a building block of protein) is found in food like meats and nuts. Because of its blood vessel-dilating effects, L-arginine supplements help lower blood pressure in pregnant women and people with hypertension (high blood pressure) (McRae, 2016).

• L-citrulline: This is another amino acid that reduces blood pressure and helps manage a condition called prehypertension, a form of mildly elevated blood pressure. People with prehypertension have an increased risk of high blood pressure, heart disease, and stroke (Allerton, 2018; Srivastava, 2021). 

Nitric oxide itself is not something you should be taking without the guidance of a healthcare professional. In the form of nitrates, it’s used as a treatment for people with chest pain associated with heart disease and those with a history of heart attacks, but it can cause dangerously low blood pressure and even death. 

We’ve talked about nitric oxide for blood pressure, but some manufacturers claim that these supplements can boost athletic performance and improve erectile function. 

The research on this is mixed, though. Studies suggest nitric oxide supplements may have promising health benefits in theory, although, so far, studies in humans are limited. Here’s what the science says about how nitric oxide supplements can improve our overall health.

1. Reduce blood pressure

A number of studies have found that nitric oxide supplements may improve key indicators of heart health. 

For example, after taking nitric oxide supplements for 30 days, people with hypertension experienced a significant decrease in resting blood pressure. They were also able to walk farther in a timed test and reported an improved quality of life (Biswas, 2015).

L-arginine supplements can reduce preeclampsia, a dangerous condition that affects up to 8% of pregnancies. Preeclampsia is a form of high blood pressure during pregnancy that can lead to devastating damage to the liver and kidneys and affect how much blood and oxygen reach the fetus. In a review of clinical trials, researchers found that pregnant women with high blood pressure and those at risk for preeclampsia who took L-arginine supplements daily had a reduced risk of developing preeclampsia and lower risk of premature birth compared to a placebo (Dorniak-Wall, 2013).

L-arginine may also have beneficial effects for insulin resistance and maintaining a healthy weight among people with diabetes (McNeal, 2016).

2. Heighten athletic performance

Many people use nitric oxide as a workout supplement. In fact, it’s one of the top five sports supplements used by U.S. Marine Corps recruits (Young, 2009). The theory goes that since nitric oxide improves blood and oxygen flow to the muscles, supplements may help you exercise for longer and recover more quickly afterward. 

First, do these supplements really boost your NO levels? Some studies say no. After testing participants’ NO levels pre- and post-supplementation and comparing the results to placebo, researchers in one small study found that the supplements had no effect on nitric oxide levels (Meirelles, 2018).  

As for whether nitric oxide truly has exercise-boosting benefits, even if you could boost it, the jury is still out. Studies show that some people experience improvements to their exercise performance after taking supplements that claim to boost nitric oxide levels, while others don’t. Other studies have found that nitric oxide is only beneficial for people who either don’t exercise or occasionally engage in aerobic exercise. People who work out regularly and take the supplements experience no benefit (Bescos, 2012). 

In one very small study, 12 men who took a nitric oxide supplement before weight lifting were able to lift more and do extra repetitions (Mosher, 2016). However, another study found it had no effect on athletic performance when taken as a pre-workout supplement (Meirelles, 2018). 

The bottom line: supplements that claim to boost your nitric oxide levels likely won’t, and they probably won’t improve your athletic performance. 

3. Enhance blood flow and erectile function

Erectile dysfunction (ED) is very common, affecting over half of men ages 40 to 70 years old. And since erections require good blood flow, and ED is often the result of disrupted blood flow to the penis, treatments that alleviate that issue might be of some use. At least that’s the theory. 

And science seems to agree. Studies in animals and in humans have shown that supplements purported to boost nitric oxide levels may, in fact, reduce symptoms of ED. 

A study of rabbits found that oral L-arginine and L-citrulline supplements increased nitric oxide levels and blood flow in these fuzzy friends, though the measurements were done in their ears (Morita, 2014). Research on rats reported that topic L-citrulline cream increased nitric oxide levels in the penis and improved erectile function, making it a promising potential add-on therapy to existing ED treatments (Davies, 2015).

Okay, it helps rabbits and rats, but what about humans? Research has found L-citrulline supplements also improved erection hardness in men with mild ED (Davies, 2015). 

In another study, 300 men with mild to severe ED were split into three groups. For 12 weeks, one group took a daily dose of L-arginine, one took tadalafil (brand name Cialis; see Important Safety Information) (a popular ED medication), and the third group used both. Across all levels of ED, taking supplements in addition to tadalafil was more effective than ED drugs alone (Gallo, 2020).

Nitric oxide supplements are generally considered safe and side effects are rare. That said, adverse reactions become more common among people taking higher doses (for example, over 9,000 mg). These side effects may include (Grimble, 2007; McNeal, 2016):

• Headache

• Diarrhea

• Nausea

• Stomach pain or bloating

• Vomiting

It’s a good idea to speak with your healthcare provider first before starting a nitric oxide supplement, particularly if you’re taking other medications or have another health condition. They can recommend an appropriate dose, depending on your goals and medical history.

You can also increase nitric oxide production through diet. Watermelon juice, beetroot juice, spinach, lettuce, nuts, meats, and seafood are all good sources of L-arginine and L-citrulline. Incorporating more of these foods into your diet may improve your nitric oxide levels (Bescos, 2012; Mosher, 2016).

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How we reviewed this article

Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

January 11, 2022

Written by

Amelia Willson

Fact checked by

Yael Cooperman, MD

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About the medical reviewer

Yael Cooperman, MD, Ro

Yael Cooperman is a physician and works as a Senior Manager, Medical Content & Education at Ro.