You've seen both on the tub: plain L-citrulline and citrulline malate. One is cheaper per gram of citrulline, the other comes with a famous add-on. Supplement marketing says the form matters. A new six-week trial in resistance-trained men says the answer is more surprising, and more limited, than the hype suggests.
The Study at a Glance
Published in 2025 in the Journal of the International Society of Sports Nutrition, the double-blind, placebo-controlled trial came from Bayat, Azizi, Behpour, and Tinsley. Thirty-three resistance-trained men were randomly assigned to one of three daily protocols:
- L-citrulline (LC): 8 g per day
- Citrulline DL-malate (CM): 12 g per day
- Placebo (PL)
All groups followed the same 6-week resistance training program. Before and after, the researchers measured:
- Strength: 1RM for hack squat and bench press
- Muscular endurance: reps to failure on hack squat, leg extension, bench press, and incline press
- Rating of perceived exertion (RPE)
- Blood markers: lactate, urea, and nitric oxide metabolites (NOx)
The Striking Finding: Upper-Body Reps
The headline result is in the upper body. When the researchers summed reps to failure on bench press and incline press, both citrulline groups beat placebo.
- LC vs. placebo: p < 0.001
- CM vs. placebo: p = 0.026
The lower body was less clear. For the combined hack squat and leg extension reps to failure, LC vs. placebo showed only a trend (p = 0.070). That is suggestive, not a confirmed win.
So the pattern is that citrulline helped you grind out more reps on pressing movements, but the evidence for the legs is weaker.
The NOx Angle
Nitric oxide metabolites (NOx) are the blood-based proxy researchers use for nitric oxide availability. Nitric oxide is linked to blood flow and the "pump" lifters chase.
The data showed:
- A significant time effect for NOx only in the LC (p = 0.014) and CM (p = 0.003) groups. Placebo showed no such change.
- For post-exercise NOx at the end of the study, CM was significantly higher than placebo (p = 0.009). LC was only marginally different (p = 0.057).
The authors' conclusion was that citrulline appears to boost both upper-body muscular endurance and the post-exercise NOx response to training, with no apparent difference between LC and CM on those outcomes.
What Citrulline Did Not Do
This part matters if you're buying for strength. The abstract reports no other between-group differences for any outcome measure. That covers:
- 1RM strength: no between-group advantage reported for hack squat or bench press
- RPE: no difference
- Lactate and urea: no difference
If your only goal is a heavier single, this study gives you no evidence that citrulline will deliver it. The benefit was in repetition performance.
Does the Form Matter?
Per the authors, there was no apparent difference between the two forms for upper-body endurance or post-exercise NOx. That leaves some nuance:
- The LC group showed the stronger statistical signal for upper-body reps (p < 0.001 vs. p = 0.026), but the paper does not claim it is superior.
- The CM group had the clearer post-exercise NOx separation from placebo.
- The doses differed (8 g vs. 12 g), so this was not a perfectly matched comparison of the molecules. Citrulline malate also contains malate, so 12 g of CM delivers less actual citrulline than 12 g of pure L-citrulline.
The practical takeaway is that you probably don't need to agonize over the form. Check the label for how much actual citrulline you're getting per serving, and compare price per effective dose.
Practical Takeaways for Lifters
Dose: The study used 8 g/day of L-citrulline or 12 g/day of citrulline malate, taken daily across six weeks of training. Those are the doses with evidence behind them here.
Timing: The abstract describes daily supplementation but not a specific pre-workout window, so the paper can't tell you whether timing around training matters. Many lifters take it before training out of habit, but treat that as convention, not a finding from this trial. Consistency over the six weeks is what was actually tested.
Who it's for:
- Lifters who care about rep performance on pressing movements, such as bodybuilders and anyone running high-rep sets
- Trained men similar to the study population
- Those who want to support nitric oxide markers around training
Who should temper expectations:
- Strength-focused lifters chasing 1RM gains
- Anyone expecting a big leg-day boost, since the lower-body result was only a trend
The Caveats
Before you restock your shelf, remember the limits:
- Small sample: 33 participants split across three groups is modest, and small trials can overstate or miss effects.
- Resistance-trained men only: the results don't automatically apply to women, beginners, or older adults.
- Short duration: six weeks tells us little about long-term effects.
- Mismatched doses: 8 g LC vs. 12 g CM complicates head-to-head conclusions.
- Blood markers aren't muscle: NOx is an indirect measure, and the paper doesn't show that higher NOx caused the extra reps.
Bottom Line
In this trial, both L-citrulline (8 g/day) and citrulline malate (12 g/day) helped resistance-trained men squeeze out more upper-body reps over six weeks and raised NOx responses, with no clear winner between forms. They didn't improve strength, RPE, lactate, or urea relative to placebo. It's promising for muscular endurance, but a single small study isn't the final word. Replication in larger and more varied groups will show how far these findings go.
