Is L-citrulline for ED safe, and does it actually work?

Dealing with erectile dysfunction (ED) can be frustrating—so much so that you’ve gone down a research rabbit hole in the name of easing your down-there difficulties. And in your quest to find a solution, you’ve likely come across plenty of content talking about “natural” treatments for ED, including an amino acid known as L-citrulline. But does L-citrulline for ED actually work? And what does research have to say about it? 

While some studies suggest that L-citrulline can offer ED (and other) benefits for males, research on the topic is quite limited. Still, however, you’re curious and want to know more. So, let’s take a closer look at L-citrulline for ED. Keep reading to learn about how the amino acid works, what research says about its potential benefits for males, and more. 

L-citrulline is a non-essential amino acid. This means that the body can produce it on its own if L-citrulline isn’t consumed through food or obtained via supplements. L-citrulline’s major role is supporting the urea cycle in the liver; this is the process of removing ammonia (which is toxic) from the body by converting it into urea, which is then excreted in urine. In other words, L-citrulline is key for getting rid of ammonia—which comes from the gut as well as the breakdown of proteins—in the body. 

 First, we need to talk about nitric oxide, a gas that is naturally produced in the body and is key for erectile function. Nitric oxide helps to facilitate erections by signaling blood vessels to widen (a process called vasodilation) and smooth muscles in the penis to relax. Importantly, L-citrulline is converted into L-arginine,  another amino acid, which, in turn, helps produce nitric oxide.  

By supporting nitric oxide production, L-citrulline can indirectly relax blood vessels and improve blood flow—a crucial component for achieving and maintaining an erection. (Friendly reminder: ED is commonly the result of problems with blood flow.) So, the thinking is that upping your intake of foods rich in L-citrulline or taking L-citrulline supplements can increase the amount of the amino acid in your body, which can then boost nitric oxide levels and blood flow to (hopefully) support erectile function. 

L-citrulline and L-arginine are sometimes combined in supplements because they are involved in similar pathways that help with blood flow and could benefit ED.

Enhance athletic performance 

While there are some conflicting results in available studies, some research has been done on L-citrulline’s effects on exercise based on the hypothesis that the amino acid may improve blood flow to the muscles. This, in turn, may enhance athletic performance in both high-intensity exercises and resistance training. Remember how L-citrulline supports nitric oxide production, which causes blood vessels to relax? Researchers believe this may improve the delivery of blood and oxygen to muscles during exercise, which then can lead to better athletic performance. Data is mixed, but some studies have found an improvement in athletic performance with L-citrulline supplementation.

Improves heart health 

As explained above, L-citrulline can increase nitric oxide production, which causes vasodilation and improves blood flow. In addition to benefiting erections, this effect can also help the heart by improving circulation and reducing blood pressure, thereby lowering the strain on the cardiovascular system and, hopefully, the risk of conditions such as hypertension (high blood pressure). 

According to a scientific review, short-term L-citrulline supplementation has been shown to reduce blood pressure in adults with pre-hypertension and hypertension. By lowering blood pressure, L-citrulline may also prevent or reduce damage to blood vessels. But more long-term research on humans is needed to conclusively determine this potential effect.

Reduces inflammation 

Prolonged high levels of inflammation can lead to a slew of health problems, including cardiovascular diseases, diabetes, arthritis, and other chronic conditions. Citrulline can help reduce certain markers of inflammation, which could mean it can have a long-term beneficial effect on numerous organ systems in the body. 

There isn’t one standard recommended dosage of L-citrulline recommended for ED, largely because there is a limited amount of scientific evidence. That said, in one study evaluating the effects of L-citrulline on ED, participants received 1.5 grams of L-citrulline orally per day. 

If you want to up your levels of L-citrulline, you have two options: Eating more foods that contain the amino acid or taking a supplement. Watermelon, for example, is considered one of the best food sources of L-citrulline. The only problem? Research suggests you need to eat quite a bit of it (2.2–3.3 pounds per day) to achieve the minimum effective dose of L-citrulline. 

A potentially easier option to boost your L-citrulline levels is taking a supplement. Once you start taking a citrulline supplement, it’s natural to wonder how long it will take to work. There aren’t many scientific studies on citrulline for ED, so it’s hard to say, but in one existing study, men took citrulline for one month to experience its benefits. Though this study was small, men reported a significant increase in self-reported erection hardness and number of sexual intercourse encounters per month.

As with any supplement, it’s important to be aware of any potential risks or side effects. Unlike prescription medications, supplements are not regulated by the Food and Drug Administration (FDA). Meaning, they do not have to go through the same rigorous testing for safety and efficacy before hitting shelves. To try to make sure the citrulline supplement you are considering taking is safe, general advice is to consider ones that have been tested by an independent third party, such as NSF International or Informed Choice. This ensures the dosage indicated on the label is correct and there aren’t toxic ingredients.

While L-citrulline is generally well-tolerated, some people do experience side effects from L-arginine, with which L-citrulline is often coupled. These side effects can include nausea, vomiting, diarrhea, headache, flushing, or numbness due to the conversion of L-arginine to byproducts by the body.

Side effects for amino acid supplements, like L-citrulline, can be especially dangerous to children, people who are pregnant, elderly individuals, or those with other medical conditions like diabetes and liver disease. Taking too much could cause an amino acid imbalance, which could negatively impact the liver and other organs like the kidneys. This is especially a risk when an amino acid like L-citrulline is taken at a high amount (more than 10 grams), so consider this your reminder to stick with the recommended dose as indicated on the supplement’s label; more does not equal better.

Since L-citrulline and L-arginine are both amino acids and work together, it can be easy to assume they work the same way—including for ED—but there are some distinct differences between the two. 

As previously explained, L-citrulline is converted into L-arginine, which produces nitric oxide and helps with blood flow. You may think that taking an L-arginine supplement is a shortcut and leads to producing nitric oxide quicker, but studies show that L-citrulline can work better than L- arginine because it’s more bioavailable and can get converted to L-arginine in multiple areas in the body. That said, both amino acids do play an important role in increasing blood flow and improving ED.

L-citrulline isn’t necessarily the best (or only) thing you can do if you have ED. There are FDA-approved options based on scientific studies, including medications known as phosphodiesterase type 5 (PDE5) inhibitors. These drugs are subject to far more regulation than supplements. Viagra (sildenafil), Cialis (tadalafil), vardenafil, and Stendra (avanafil) are all examples of PDE5 inhibitors used for ED. These medications work in part by increasing blood flow to the penis—something they have in common with the way L-citrulline supplements are proposed to work, but there is far more scientific evidence supporting the effectiveness and safety of these prescription drugs for erectile function.  

You can also find certain PDE5 inhibitors in other non-pill formulations. One example is Ro Sparks, a 2-in-1 sublingual treatment that contains both sildenafil and tadalafil (the active ingredients in Viagra and Cialis, respectively) and dissolves under your tongue for fast-acting effects. Then there are Ro’s Daily Rise Gummies, which contain 7 mg of tadalafil in each fruit-flavored gummy. 

Not ready to get an Rx? You can start with some diet and lifestyle modifications. Maintaining a healthy diet, exercising regularly, getting enough sleep, and looking after your mental health have all been shown to help with ED.

If you are experiencing ED regularly, taking a citrulline supplement could help because it is theorized to improve blood flow. Besides helping with ED, L-citrulline may offer additional benefits for males, including supporting heart health and athletic performance. Keep in mind, though, that research on L-citrulline for ED and other potential perks is rather limited. So, more research is needed to truly determine its effects on humans. 

At the end of the day, your best (and safest) bet is to consult a healthcare provider if you’re dealing with ED, as they can determine what might be causing your symptoms and help find a solution that’s a fit for you. 

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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.

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Current version

November 26, 2024

Written by

Emily Laurence

Fact checked by

Raagini Yedidi, MD

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About the medical reviewer

Raagini Yedidi, MD

Raagini Yedidi, MD, is an internal medicine resident and medical reviewer for Ro.