L-Citrulline and Nitric Oxide Explained: The Lead Ingredient in Maxorin
Quick answerL-citrulline is an amino acid the body turns into arginine, which vessel walls use to make nitric oxide. In a small study, 1.5 g a day for one month improved erection hardness in 50% of men with mild ED, versus 8% on placebo. Citrulline leads the Maxorin blend, so it holds at most 570 mg per capsule.
What is nitric oxide and why does it matter?
Nitric oxide is a small gas molecule that tells blood vessels to relax. When the muscle in a vessel wall eases, the vessel widens and blood flows more freely. That simple signal matters all over the body.
Erections rely on the same signal. Blood vessels in the penis relax and fill with blood. So anything that supports healthy vessel lining matters for sexual health as much as for the heart.
The body makes nitric oxide from the amino acid arginine. L-citrulline is one step back in that chain, which is why it leads the Maxorin blend.
How does L-citrulline become nitric oxide?
L-citrulline does not make nitric oxide directly. It moves through a short chain of steps first. The body can also recycle it, which keeps the chain turning.
You swallow citrulline
It passes through the gut and liver mostly intact.
The kidneys convert it
Citrulline is turned into arginine and released into the blood.
Vessel walls use arginine
An enzyme in the vessel lining turns arginine into nitric oxide.
Vessels relax
Nitric oxide signals the muscle in the vessel wall to ease. Citrulline is left over and can be used again.
Why use L-citrulline instead of L-arginine?
Arginine seems like the obvious choice, since it is the direct building block. The catch is absorption. Much swallowed arginine is broken down in the gut and liver before it reaches the blood.
The Schwedhelm study
Researchers gave 20 healthy volunteers citrulline, arginine or placebo, at doses up to 3 g twice a day. Citrulline raised blood arginine more effectively than arginine itself (Schwedhelm et al., 2008). That is the main reason many formulas now use citrulline.
What that study did not show
The trial measured blood levels and markers of nitric oxide. It did not test sexual function. Higher arginine in the blood is a step in the chain, not proof of any effect you can feel.
What did the Cormio L-citrulline study find?
One trial in men is quoted more than any other for this ingredient. It is short and small, so it is worth reading closely before leaning on it.
The design
Twenty-four men with mild ED took 1.5 g of L-citrulline a day for one month (Cormio et al., 2011). The study also ran a placebo month for comparison. The researchers tracked an erection hardness score.
The result
Half the men (50%) improved their hardness score while taking citrulline. On placebo, 8% did. That is a clear gap for such a short study.
The limits
The study was small, and it was single-blind, so the researchers knew who got what. The men had mild ED only. Larger, double-blind trials would give a firmer answer.
L-citrulline leads the Maxorin blend
One capsule a day with L-citrulline first in a 570 mg blend, plus niacin 20 mg and zinc 11 mg. From $49 a bottle, with a 60-day money-back guarantee.
How much L-citrulline is in a Maxorin capsule?
The exact amount of L-citrulline in Maxorin is not published. The label gives one weight for the whole blend: 570 mg. Under 21 CFR 101.36, blend ingredients are listed in order of weight (21 CFR 101.36).
Citrulline is first, so it is the largest part. Its ceiling is the full 570 mg, but five other ingredients share that weight too. The real amount is lower than 570 mg.
Compare that with the study. The whole blend is 38% of the 1.5 g daily dose used by Cormio. So Maxorin does not match the studied citrulline dose. Our post on how to read a proprietary blend label shows the ceiling math for all six.
How does L-citrulline compare with other nitric oxide ingredients?
Several ingredients in this category touch the nitric oxide pathway. The evidence and doses differ a lot. Here is how they line up with the Maxorin label.
| Ingredient | Link to nitric oxide | Dose studied | In Maxorin |
|---|---|---|---|
| L-Citrulline | Turned into arginine, then nitric oxide | 1.5 g a day (Cormio et al., 2011) | First in blend, at most 570 mg |
| L-Arginine | Direct building block for nitric oxide | Up to 3 g twice a day (blood levels only) (Schwedhelm et al., 2008) | Not in the formula |
| Pine bark extract | Studied only alongside arginine | 80-120 mg with 1.7 g arginine (Stanislavov & Nikolova, 2003) | Third in blend, at most 190 mg |
| Grape skin extract | Source of resveratrol; artery widening | 30-270 mg pure resveratrol (Wong et al., 2011) | Fifth in blend, at most 114 mg; resveratrol not stated |
What sits beside L-citrulline in the Maxorin blend?
Citrulline shares the 570 mg blend with five other ingredients. Each has its own small body of research, and each takes a smaller share of the weight than citrulline.
L-carnitine
Carnitine is second in the list, so it holds at most 285 mg. A trial in men aged 60-74 used about 4 g a day of two carnitine forms for 6 months (Cavallini et al., 2004). Gram doses can cause nausea and a fishy body odor (NIH ODS, Carnitine).
Maca and saffron
Maca root was studied for sexual desire at 1.5 or 3 g a day (Gonzales et al., 2002). Saffron trials used 30-60 mg a day (Maleki-Saghooni et al., 2018). Saffron is last in the blend, with a ceiling of 95 mg, so it could fit that range. Its real amount is not published.
Niacin and zinc
Outside the blend, the label prints niacin 20 mg and zinc 11 mg. These are the two amounts you can check. See the Supplement Facts page for the full panel.
Who should check with a doctor before taking L-citrulline?
Most healthy adults handle citrulline well, and watermelon is a common food source. Still, a few groups need medical advice before they take it as a supplement.
Nitrates and blood pressure drugs
Citrulline feeds the pathway that relaxes blood vessels. If you take nitrate heart drugs or blood pressure medicine, the effects could add up. Ask your doctor before starting.
New erection problems
New ED can be an early heart warning. In 92,757 men, ED was linked to a 44% higher risk of cardiovascular events (Vlachopoulos et al., 2013). Leading causes include diabetes, heart disease and high blood pressure (NIDDK, causes of ED). See a doctor rather than trying to self-treat.
Buy from a known source
The FDA has found hidden sildenafil and tadalafil in many products sold as sexual enhancement supplements (FDA, sexual enhancement notifications). Those drugs can drop blood pressure dangerously with nitrates. Buy from the authorized seller, and read the side effects page for the full formula.
How can food and habits support nitric oxide?
Everyday habits support nitric oxide too, and they help the heart at the same time. None of them need a prescription.
Eat watermelon
The name citrulline comes from the watermelon's Latin name. It is a classic food source.
Add leafy greens
Spinach, arugula and beets supply nitrate, a second route to nitric oxide.
Move most days
Blood flow during exercise prompts vessel walls to make more nitric oxide.
Skip tobacco
Smoking damages the vessel lining that makes nitric oxide.
Our male performance guide puts these habits in order. For the two printed amounts on the label, read what 11 mg of zinc and 20 mg of niacin mean. The ingredients page covers the whole formula.
L-citrulline and nitric oxide FAQ
What is L-citrulline?
It is an amino acid. The body makes some on its own, and watermelon is a well-known food source. The kidneys turn it into arginine.
How does L-citrulline relate to nitric oxide?
Citrulline becomes arginine, and an enzyme in the lining of blood vessels uses arginine to make nitric oxide. Nitric oxide signals the vessel wall to relax.
Why use citrulline instead of arginine?
In 20 healthy volunteers, oral citrulline raised blood arginine more effectively than arginine itself. Much swallowed arginine is broken down before it reaches the blood.
How much L-citrulline did the main study use?
The Cormio study used 1.5 g a day for one month in 24 men with mild ED. It was small and single-blind.
How much L-citrulline is in Maxorin?
The exact amount is not published. It is first in a 570 mg blend, so it can be no more than 570 mg, and the other five blend ingredients share that weight.
Can I take L-citrulline with blood pressure medicine?
Ask your doctor first. Citrulline feeds the nitric oxide pathway, which relaxes blood vessels. That can add to blood pressure drugs or nitrates.
Does L-citrulline treat erectile dysfunction?
No. ED is a medical condition, and a dietary supplement cannot treat it. New erection problems can be an early heart warning and need a doctor's visit.