Citrulline malate is a sports supplement that combines L-citrulline, an amino acid, with malic acid, a compound found naturally in apples and other fruits. It’s widely used as a pre-workout ingredient to improve endurance during strength training, reduce post-exercise soreness, and support blood flow. Most research has used an 8-gram dose taken about an hour before exercise, and a meta-analysis of the available evidence found it increases repetition volume by roughly 6.4% compared to a placebo.
What’s Actually in It
The supplement is a simple two-part compound. L-citrulline is a non-essential amino acid your body already produces in small amounts. It plays a key role in the urea cycle, the process your liver uses to clear ammonia (a waste product of protein metabolism) from the blood. Malic acid is an organic acid involved in energy production at the cellular level, specifically in the series of chemical reactions your mitochondria use to generate fuel from food.
Products are typically sold in a 2:1 ratio, meaning two parts citrulline to one part malic acid. So in an 8-gram dose of citrulline malate at this ratio, you’re getting roughly 5.3 grams of actual citrulline and 2.7 grams of malic acid. This matters because some labels list citrulline malate content without specifying the ratio, which can make it hard to compare products or match the doses used in clinical research.
How It Works in Your Body
Once you consume citrulline malate, the citrulline portion is absorbed in the gut and converted to another amino acid, arginine, primarily in the kidneys. Arginine is the direct precursor to nitric oxide, a molecule that relaxes and widens blood vessels. This increased blood flow delivers more oxygen and nutrients to working muscles during exercise.
Citrulline is actually more effective at raising arginine levels than taking arginine directly. Supplemental arginine gets heavily broken down during digestion before it ever reaches the bloodstream, while citrulline bypasses that breakdown and converts to arginine after absorption. The citrulline component also supports the urea cycle, helping your body clear ammonia more efficiently. Ammonia accumulates during intense exercise and contributes to fatigue, so faster clearance can delay the point at which your muscles give out. The malic acid component contributes to aerobic energy production, though its independent effect is less studied than citrulline’s.
Performance Benefits
The strongest evidence for citrulline malate is in resistance training. A systematic review and meta-analysis found that supplementing with 6 to 8 grams about 40 to 60 minutes before exercise increased total repetitions by an average of 3 reps, or about 6.4%, compared to a placebo. The effect was small but statistically significant. When the researchers broke it down by body region, lower-body exercises showed a trend toward a larger benefit (8.1% more reps) while upper-body exercises showed a smaller, non-significant improvement (5.7%).
In practical terms, this means citrulline malate is most likely to make a noticeable difference during high-rep, fatigue-driven training. If you’re doing sets of 3 heavy squats, an extra fraction of a rep isn’t meaningful. But across multiple sets of 10 to 15 reps, squeezing out a few more reps per set adds up to meaningfully more training volume over a session. That accumulated volume is one of the primary drivers of muscle growth over time.
Research on endurance exercise like cycling is less consistent. Some studies show modest improvements in time-trial performance, while others find no effect. The supplement appears better suited to repeated high-intensity efforts than steady-state cardio.
Effects on Muscle Soreness
Citrulline malate also appears to reduce delayed-onset muscle soreness, particularly in the first 24 hours after a hard workout. A meta-analysis of seven studies found a significant reduction in perceived soreness at the 24-hour mark, with a large effect size. At 48 hours, the picture was more mixed. Most individual studies pointed toward reduced soreness, but one outlier study skewed the pooled results. When that study was excluded in a sensitivity analysis, the 48-hour benefit became statistically significant as well.
By 72 hours post-exercise, citrulline’s effect on soreness fades to nothing. This suggests the supplement helps most with that acute next-day stiffness rather than the lingering soreness from unusually demanding sessions. The likely mechanism is improved blood flow and faster waste clearance from damaged muscle tissue, though the exact pathway isn’t fully confirmed.
Dosing and Timing
The standard research dose is 8 grams of citrulline malate taken as a single dose about 60 minutes before exercise. This is the amount used in most trials showing positive results for strength training performance. Studies have tested doses ranging from 3 to 12 grams at 40 to 120 minutes before exercise, but 6 to 8 grams taken 40 to 60 minutes beforehand is the most common and well-supported protocol.
It’s worth noting that many commercial pre-workout blends contain citrulline, but often at lower doses than what the research supports. A survey of popular pre-workout products found an average citrulline dose of about 4 grams, roughly half of the 8-gram dose studied in most clinical trials. If you’re relying on a pre-workout blend for your citrulline, check the label to see whether the dose matches what the evidence actually supports.
Citrulline in Food
Watermelon is the richest dietary source of citrulline, which is how the amino acid got its name (Citrullus is the Latin genus for watermelon). The rind contains the highest concentration, roughly 60 to 500 milligrams per 100 grams. The red flesh has less, between 40 and 160 milligrams per 100 grams.
These amounts are far below supplemental doses. To reach even the minimum effective dose of about 3 grams of citrulline from food, you’d need to eat 2.5 to 5 kilograms of watermelon flesh, or 1 to 3 kilograms of rind, per day. That’s roughly 5 to 11 pounds of watermelon just to hit the low end. For the 8-gram dose used in strength training research, food sources are simply impractical.
Citrulline Malate vs. L-Citrulline
You’ll find both citrulline malate and plain L-citrulline on supplement shelves. The key difference is straightforward: citrulline malate includes malic acid, while L-citrulline is the amino acid alone. Because citrulline malate contains malic acid as part of its weight, you get less actual citrulline per gram. In a 2:1 citrulline malate product, about a third of the weight is malic acid.
If your primary goal is boosting nitric oxide and blood flow, plain L-citrulline gives you more citrulline gram for gram. If you want to replicate what most strength training studies have tested, citrulline malate at 8 grams is the more directly supported choice. The malic acid component may offer a small additional benefit for energy production, but no study has isolated that effect convincingly enough to call it a deciding factor. Either form raises arginine and nitric oxide levels effectively.
Side Effects and Safety
Citrulline malate is well tolerated at the doses used in research. The 8-gram pre-exercise dose has been used across multiple studies in both men and women without reports of serious adverse effects. The most commonly noted side effect is mild gastrointestinal discomfort, which can happen with any amino acid supplement taken on a relatively empty stomach before training. Taking it with a small amount of food or diluting it well in water can help. The upper end of citrulline dosing explored in research is 12 grams per day, which has also been used without significant safety concerns.