L-arginine and L-citrulline show up together in almost every circulation or blood-pressure-support formula, including BloodPril. They're closely related, work toward the same goal, and are often included as a pair rather than a substitute for one another. Here's what actually separates them.
L-Arginine: the direct building block
L-arginine is an amino acid your body uses directly to produce nitric oxide, via an enzyme called nitric oxide synthase. Because it's the direct precursor, taking L-arginine can raise blood arginine levels relatively quickly.
The catch: a large portion of orally consumed L-arginine gets broken down in the liver and gut before it ever reaches the bloodstream — a limitation known as poor bioavailability. That's one reason formulas often pair it with a second source.
L-Citrulline: the longer-lasting source
L-citrulline takes an indirect route. It's absorbed in the small intestine, bypasses the liver breakdown that limits arginine, and is converted into L-arginine by the kidneys. The result is a slower, steadier rise in blood arginine levels that lasts longer than arginine supplementation alone.
In practical terms, citrulline is often described as providing more sustained support for nitric oxide production, while arginine offers a more direct — but shorter-lived — contribution.
Why formulas combine them
Because arginine acts quickly but degrades fast, and citrulline acts more slowly but lasts longer, combining the two is a common strategy to support nitric oxide availability across more of the day rather than in a single short spike. This is the logic behind BloodPril's formula, which combines L-Citrulline DL-Malate with two forms of L-arginine — L-Arginine (Alpha-Ketoglutarate dihydrate) and L-Arginine HCl.
See how all three amino acids are combined in a single 500 mg daily blend.
View the BloodPril FormulaA quick side-by-side
- Speed: L-arginine acts more quickly; L-citrulline builds more gradually.
- Duration: L-citrulline's effect on blood arginine levels tends to last longer.
- Bioavailability: L-citrulline is less affected by liver breakdown than oral L-arginine.
- Common use: Often combined rather than used alone, for both fast and sustained support.
As with any amino acid research, these findings describe how the ingredients behave individually — they aren't a guarantee of results from any specific finished product. For more on what nitric oxide actually does once it's produced, see our explainer on nitric oxide and blood pressure.