We know – the world of fitness supplements can be confusing.

You probably know that protein powder is an easy way to reach your calorie and macronutrient goals and that creatine is a safe and effective way to increase power and anaerobic capacity.

That’s roughly where the consensus ends when it comes to fitness supplements, and for those of us looking to improve workout performance, it can be hard to know what else meets the approval of the scientific community at large.

Enter L-arginine, (also just called “arginine”) an amino acid that’s been linked to everything from better workouts to stronger erections. Can it improve your PRs, or is it just another well-packaged bottle of powdered snake oil?

The Claims

As a conditionally essential amino acid, the body does a decent job of producing arginine on its own, but there could be some situations where it’s useful to supplement it.

The most common claim surrounding arginine is its purported abilities of vasolidation, meaning that it “opens up” veins and arteries and makes it easier for blood to flow freely throughout your body. This would be because it is a precursor to nitric oxide, a known vasolidator.

Following on from that claim, arginine should be able to improve workout performance and decrease the odds of experiencing hypertension, deep vein thrombosis, erectile dysfunction, and other problems that are related to blood flow.

That is, if it’s true.

The Evidence

“L-arginine tends to be marketed towards any physical activity, since the theoretical increase in nitric oxide should benefit anything related to blood flow,” says Kurtis Frank, the research director of the independent nutrition research organization, Examine.com. “For the most part, it seems to favor CrossFit®-style activities; things that involve muscular contraction in a moderate rep range. It doesn’t seem to provide any major benefit to long distance stuff nor maximal power activities like sprinting and heavy lifting.”

When it comes to nitric oxide supplements, there’s something of a “Big Four”: L-arginine, L-citrulline, agmatine, and nitrates. Antioxidants also indirectly aid nitric oxide and are often used alongside the Big Four.

The problem, in Frank’s own words, is that arginine is the “shittiest” nitric oxide supplement of the bunch. It’s not even worth taking it with the other NO supplements, since they’d be competing for the same mechanism. If taken side by side, he explains, it’d end up being a one-plus-one-plus-one equals one-type scenario.

The question, then, is what’s the smartest way to boost nitric oxide?

 “I’d recommend L-citrulline or agmatine over L-arginine any day, for workouts and for the general health benefits,” says Frank. “Agmatine could be seen as the healthiest, since it has other mechanisms in addition to the NO production, like neuronal health.”

Focusing on L-citrulline or agmatine is also likely to benefit your wallet, since dedicated nitric oxide supplements are notorious for trying to increase profits by adding twenty somewhat relevant ingredients, while they usually only have a couple of ingredients that are truly effective. (Frank likens NO supplements to “fat burners” in that regard.)

Arginine, it turns out, is a weak pick for the benefits a buyer is probably after. The link it has to actually boosting nitric oxide is weak, and the initial belief that it’s a solid NO supplement is sometimes known as “The Arginine paradox.”

“L-arginine was initially thought to increase NO because it’s a precursor – you need some arginine for the enzymes that make NO,” says Frank. “But when you put more arginine into a system, NO doesn’t necessarily increase. It turned out that’s because it’s not just a substrate, it works mostly through the A2-andrenergic receptor. Agmatine is a lot more potent in the way it acts on this receptor, and L-citrulline, while it works in a more similar manner to L-arginine, does a much better job of absorbing through the intestines. By the way, that’s why a lot of people get ‘pre-workout’ shits; they combine caffeine with L-arginine, both of which can go right through you.”

But Doesn’t L-Arginine Increase My Muscle Size?

Finally, L-arginine is also thought by many to increase the body’s production of the anabolic human growth hormone (HGH) and creatine.

But arginine doesn’t do anything for your creatine production unless you’re already deficient in arginine, and it’s extremely unlikely that you are. (Remember that the body can make its own arginine, plus it’s present in most sources of protein.)

And as far as growth hormone goes, arginine and creatine do technically increase its production after a workout, but for such a small time frame that it’s doubtful it’ll have any practical effect on your body. So don’t turn to L-arginine to give you Stallone-like HGH levels.

The Takeaway

This science is a little dense, but here’s the take-home lesson.

First, if lowering your risk of hypertension by improving your blood flow, you’re better off talking to your doctor and considering pharmaceuticals and ACE inhibitors. Supplements, after all, aren’t medications.

But, if you’re interested in a nitric oxide-boosting, blood vessel-opening pre-workout supplement, you’re better off turning to L-citrulline or agmatine, the latter of which might be the better choice. About three grams per day of either is a safe and effective dose.

Featured image via @_king_tunde_

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Nick is a content producer and journalist with over seven years’ experience reporting on four continents. His first articles about health were on a cholera outbreak in rural Kenya while he was reporting for a French humanitarian organization. His next writing job was covering the nightlife scene in Shanghai. He’s written on a lot of different kinds of things, but his passion for health ultimately led him to cover it full time.Shanghai was where he managed to publish his first health related article (it was on managing diarrhea), he then went on to produce a radio documentary about bodybuilding in Australia before he finished his Master’s degrees in Journalism and International Relations and headed to New York City. Here, he’s been writing on health full time for more than five years for outlets like Men's Health, VICE, and Popular Science.Nick’s interest in health kind of comes from an existential angle: how are we meant to live? How do we reach our potential? Does the body influence the mind? (Believe it or not, his politics Master’s focused on religion.)Questions like these took him through a lot of different areas of health and fitness like gymnastics, vegetarianism, kettlebell training, fasting, CrossFit, Paleo, and so on, until he realized (or decided) that strength training fit best with the ideas of continuous, measurable self improvement.At BarBend his writing focuses a little more on nutrition and long-form content with a heaping dose of strength training. His underlying belief is in the middle path: you don’t have to count every calorie and complete every workout in order to benefit from a healthy lifestyle and a stronger body. Plus, big traps are cool.