Tl;dr version of L-Citrulline vs L-Arginine:
- Primary effect: Increases production of Nitric Oxide.
- Nitric Oxide improves blood flow by expanding blood vessels.
- L-Citrulline is a precursor of Arginine.
- Supplementation-wise L-Citrulline seems to outperform Arginine.
- Both are well-tolerated at regular and even high doses.
- Minimum effective doses – 4g.
- Maximum effective doses – 10g.
L-Citrulline vs L-Arginine Introduction
Both Citrulline and Arginine are widely used in numerous supplements and preworkouts (e.g. Sicario) with the same goal in mind – increasing pumps. Both are purported to increase Nitric Oxide production in the body during workouts. Nitric Oxide, in turn, has many interesting effects. However, the one most commonly cited effect in fitness circles is vasodilation.
Vasodilation is the expansion of blood vessels in the body. Expanded blood vessels improve blood flow by allowing larger quantities of blood cells to pass through. Thus, Nitric Oxide increasing products (such as L-Citrulline vs L-Arginine) are often touted to improve performance and improve “pumps”. There is no clear scientific consensus on the former. However, Nitric Oxide supplement may improve performance in all but well-trained subjects.
I think the second study might have nailed it, to be honest. It would make perfect sense that something that is supposed to improve blood flow might have diminishing returns as fitness level increases. After all, good measures of overall fitness could be blood-flow-related parameters.
However, “pumps” are not a scientifically studied object, therefore finding studies that would measure L-Citrulline vs L-Arginine in that regard is difficult. Going by anecdotal evidence – L-Citrulline does work for “pumps”.
How does L-Citrulline and L-Arginine work?
L-Citrulline and L-Arginine are closely related and there are numerous conversions from one to another. Here’s an extremely simplified several step process for the conversion of L-Citrulline:
- L-Citrulline enters the body.
- L-Citrulline is converted into L-Arginine in the kidneys.
- Some Arginine is moved into blood vessels for vasodilation through the cGMP pathway.
- Some Arginine is moved into muscles for muscle protein synthesis and activates mTOR.
- Byproducts of the NOS conversion are converted back into Citrulline.
Supposedly, L-Arginine supplementation should skip the first two steps and go straight into the bloodstream, making it superior. Basically, both of these supplements would be pretty much two sides of the same coin with one having a longer path for synthesis. Additionally, L-Arginine is a lot more abundant in the natural world while L-Citrulline is only reasonably concentrated in watermelons.
L-Citrulline vs L-Arginine: Which is more effective?
For a long time, L-Arginine was considered the better version of the two. After all, why supplement something that requires synthesis in the body if you can get the final product? However, recent research has cast a shadow on the supplementation of L-Arginine for vasodilation and muscular endurance purposes.
It seems that oral L-Arginine supplementation might be prone to being essentially destroyed by the liver and intestinal tract before it gets to have an effect. However, not all of the L-Arginine is destroyed – only about 50%. Yet, very little to no L-Citrulline is destroyed in the process.
Additionally, L-Citrulline increases bioavailability of supplemental L-Arginine which indicates that using both may have synergistic effects. However, since there is a maximum effective dose of 10g, there seems to be little reason to combine both. Outside of very unique scenarios, pure L-Citrulline supplementation is going to be more effective.
It seems it might be time for L-Arginine to stand aside. If you want the best skin splitting pumps, pick pure L-Citrulline over L-Arginine. Even if the effects were exactly the same, L-Citrulline is 50% more effective at producing NO2 which is what you want!