Guide · amino acids
L-arginine vs L-citrulline: which one raises arginine more?
L-arginine vs L-citrulline comes down to the route. Arginine is the amino acid your vessels use to make nitric oxide; citrulline is turned into arginine by the kidneys. Taken by mouth, citrulline raised blood arginine more than arginine itself did. Both trimmed blood pressure slightly in trials at grams a day, far above what a Melonex capsule holds.
Written by the Melonex label deskUpdated
Side by side01
What is the difference between L-arginine and L-citrulline?
L-arginine is the amino acid that nitric oxide synthase uses to make nitric oxide. L-citrulline is a close cousin that the body turns back into arginine, and it is also left over each time nitric oxide is made (Cziraki 2020, arginine-NO pathway).
Arginine is semiessential: the body makes some, and protein foods supply the rest (Health Library, Arginine). Citrulline is rare in food outside watermelon, which gave it its name (Khalaf 2019, arginine and citrulline) (Aguayo 2021, L-citrulline review).
The bigger difference is what happens after you swallow them. That is where citrulline pulls ahead.
| Point | L-arginine | L-citrulline |
|---|---|---|
| Role | Raw material for nitric oxide (Cziraki 2020, arginine-NO pathway) | Converted to arginine in the kidneys (Aguayo 2021, L-citrulline review) |
| Main food source | Plant and animal protein (Health Library, Arginine) | Watermelon, flesh and rind (Aguayo 2021, L-citrulline review) |
| Doses in blood pressure trials | 4-24 g a day (Dong 2011, arginine meta-analysis) | 3-9 g a day (Barkhidarian 2019, citrulline meta-analysis) |
| Pooled blood pressure change | About 5.39/2.66 mm Hg lower | About 4.1 mm Hg lower systolic; diastolic not significant |
| Stomach at high doses | Nausea, vomiting or diarrhea reported (Aguayo 2021, L-citrulline review) | No GI effects even at 15 g in short studies (Aguayo 2021, L-citrulline review) |
| In one Melonex capsule | Two forms, at most about 333 mg together | Citrulline malate, about 167-500 mg |
The route02
How does the body turn citrulline into arginine?
The kidneys turn citrulline into arginine. About 83% of the citrulline they take up comes out as arginine, which then enters the blood (Aguayo 2021, L-citrulline review).
Citrulline is not broken down by the liver or the gut on the way in, so most of a dose reaches the kidneys intact (Aguayo 2021, L-citrulline review). Swallowed arginine has a rougher trip, and less of it reaches the circulation.
The loop then closes. When nitric oxide synthase uses arginine, it releases nitric oxide plus citrulline, which can be recycled again (Cziraki 2020, arginine-NO pathway).
Swallowed citrulline
Passes the gut and liver largely untouched.
Kidneys
Convert most of it to arginine.
Blood arginine rises
Vessel walls use it to make nitric oxide.
Citrulline again
Released each time nitric oxide is made.
Head to head03
Which raises blood arginine more, citrulline or arginine?
Citrulline does. In a placebo-controlled study of six dosing plans, oral L-citrulline raised blood arginine more effectively than oral L-arginine, and the rise grew with the dose (Schwedhelm 2008, citrulline kinetics).
The top citrulline plan in that study, 3 g twice a day, also kept arginine higher between doses (Schwedhelm 2008, citrulline kinetics). That is 6 g a day, many times what a Melonex capsule could hold.
Putting citrulline first in a blend follows the research on absorption. It does not tell you the amount is enough to change anything.
Blood pressure trials04
Do arginine or citrulline lower blood pressure in trials?
Both lowered blood pressure a little in pooled trials, at doses measured in grams. Arginine at 4 to 24 g a day cut readings by about 5.39/2.66 mm Hg across 11 trials and 387 people (Dong 2011, arginine meta-analysis).
Citrulline at 3 to 9 g a day cut systolic pressure by about 4.1 mm Hg in 8 trials, and the diastolic change was not significant (Barkhidarian 2019, citrulline meta-analysis). At 6 g a day or more, diastolic fell by about 2.75 mm Hg (Barkhidarian 2019, citrulline meta-analysis).
A 2019 review called the arginine result the firmer one and the citrulline effect "more questionable", since one citrulline meta-analysis found no clear change (Khalaf 2019, arginine and citrulline).
- Arginine: larger pooled change, larger doses, more stomach upset
- Citrulline: smaller doses, gentler on the gut, mixed pooled results
- Neither was tested at under 1 g a day
- Neither is a blood pressure medicine
The vessel-relaxing step is explained in nitric oxide basics.
Tolerance05
Is citrulline easier on the stomach than arginine?
Yes, in short studies citrulline was well tolerated, with no stomach or gut side effects even at a single 15 g dose. High doses of arginine caused nausea, vomiting or diarrhea (Aguayo 2021, L-citrulline review).
Mayo Clinic adds bloating, abdominal pain, gout and headache to the arginine list, and notes worse asthma in some people (Mayo Clinic, L-arginine).
At the small amounts in a Melonex capsule, stomach trouble is less likely from either one. Stop and call your doctor if it happens anyway.
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See packsWorkouts06
Is citrulline or arginine better for exercise?
Citrulline has the better exercise data, though the effect is small. Twelve placebo-controlled studies with 198 people gave at least 3 g of citrulline before testing and found a slight gain in high-intensity strength and power (Trexler 2019, citrulline exercise).
The authors say the gain may matter mainly to high-level athletes (Trexler 2019, citrulline exercise). For arginine, the Health Library finds no evidence that it improves athletic performance (Health Library, Arginine).
Melonex is sold for heart and circulation support, not for workouts, and its dose sits below the 3 g used in those studies.
Safety07
Who should avoid arginine and citrulline supplements?
Anyone who has had a heart attack should avoid arginine unless a cardiologist says otherwise. The VINTAGE MI trial stopped early after six deaths on arginine and none on placebo (VINTAGE MI trial, JAMA 2006).
Both amino acids can add to blood pressure drugs, nitrates and erectile-dysfunction drugs, so the drop can go too far (Mayo Clinic, L-arginine). Pregnant or nursing women and anyone under 18 should ask a physician first, as the Melonex label says.
An amino acid is not a replacement for a drug your doctor chose. Ask before you add either one, and bring the label along. More on supplements and heart medicines.
In Melonex08
Why does Melonex combine arginine and citrulline?
Melonex puts citrulline first and two arginine forms after it, inside one 500 mg blend. The label gives no reason, but the order matches the absorption research: citrulline as the main source, arginine as a direct one.
The split is hidden. Citrulline malate holds about 167 to 500 mg a capsule, and the two arginine lines share at most about 333 mg. Two capsules give 1 g of blend a day, against 3 g or more in every trial above.
Each weight also includes a salt partner, so the pure amino acids are less again. The line-by-line math is on the Melonex dose check, and citrulline gets its own profile at L-citrulline DL-malate.
FAQ09
Arginine vs citrulline questions
Why is it called citrulline?
Citrulline takes its name from Citrullus lanatus, the scientific name of watermelon, where it was first found. Watermelon holds about 0.7 to 3.6 g of citrulline per kilogram of fresh fruit, depending on the variety, in both flesh and rind (Aguayo 2021, L-citrulline review).
Can you get enough citrulline from watermelon?
Not easily. At 0.7 to 3.6 g per kilogram of fresh fruit (Aguayo 2021, L-citrulline review), reaching the 3 g used in trials would take about a kilogram of watermelon or more. Citrulline is rare in other foods (Khalaf 2019, arginine and citrulline).
Does the body make its own citrulline?
Yes. Each time nitric oxide synthase turns arginine into nitric oxide, it releases citrulline too. An enzyme called DDAH also makes citrulline when it breaks down ADMA, a natural blocker of nitric oxide (Cziraki 2020, arginine-NO pathway).
Is L-citrulline DL-malate the same as plain L-citrulline?
It is citrulline bound to malic acid. The citrulline is the same, but part of the weight is the malate partner. So a line of citrulline malate holds less citrulline than its weight suggests.
Does the heart attack warning for arginine also apply to citrulline?
The VINTAGE MI trial tested arginine, not citrulline (VINTAGE MI trial, JAMA 2006). But citrulline is turned into arginine in the body (Aguayo 2021, L-citrulline review), so anyone who has had a heart attack should ask a cardiologist before taking either one.
Which works better for blood pressure, arginine or citrulline?
Pooled trials found a slightly larger drop with arginine, about 5.39/2.66 mm Hg at 4-24 g a day, than with citrulline, about 4.1 mm Hg systolic at 3-9 g (Dong 2011, arginine meta-analysis) (Barkhidarian 2019, citrulline meta-analysis). Neither is a substitute for medical care.
Is it safe to take arginine and citrulline together?
Our sources tested them one at a time, so the pair at these amounts is not well studied. Melonex combines them at under 1 g of blend a day. The same cautions apply to both: ask first if you take heart or blood pressure drugs.
Who wrote this10
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Pages built from the label, the sales page and linked NIH, FDA, AHA, CDC, FTC and peer-reviewed sources.
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