Comprehensive Breakdown of The Science Behind L-Citrulline

November 26, 2025

The Science Behind L-Citrulline: Pump with Purpose

L-Citrulline has become a star ingredient in pre-workout supplements for its ability to deliver muscle pumps and performance benefits. But what exactly is L-citrulline, and why do products like Essence of Hormes pack a full 10 g dose per serving? In this article, we’ll explore the science of L-citrulline – how it works in the body, how it compares to alternatives like citrulline malate and L-arginine, and what research says about its benefits. We’ll also see how a 10-gram dose stacks up against other popular pre-workouts. By the end, you’ll understand why pure L-citrulline helps you “pump with purpose,” backed by clinical studies and peer-reviewed research.

What Is L-Citrulline and How Does It Work?

L-Citrulline is a non-essential amino acid named after Citrullus vulgaris (watermelon), from which it was first isolated. Unlike amino acids that build proteins, citrulline plays a unique role in the body’s production of nitric oxide (NO)[1][2]. When you ingest L-citrulline, your kidneys convert it into L-arginine, which is then used to generate nitric oxide.

Nitric Oxide & Vasodilation: NO is a signaling molecule that causes vasodilation, meaning it relaxes and widens blood vessels[1]. This increases blood flow throughout the body – including to your muscles during exercise. Improved blood circulation leads to the famed “muscle pump” (that tight, full feeling in muscles after intense reps) and better delivery of oxygen and nutrients to working muscles[3]. In simple terms, more nitric oxide means a better pump and potentially better performance.
Beyond the Pump – Endurance and Recovery: By boosting blood flow, nitric oxide may help you push through more reps and recover faster. Muscles get more oxygen during your workout and more nutrients afterward for recovery[4]. Many athletes report enhanced muscle endurance and reduced fatigue with effective NO boosters. (We’ll dive into specific studies on performance and recovery benefits later.)

Notably, getting enough L-citrulline from diet alone is impractical – for example, watermelon is rich in citrulline, but a typical slice provides only a few hundred milligrams. Supplements are needed to reach effective doses (usually several grams) for performance effects[5].

L-Citrulline vs. L-Arginine: Why Not Just Arginine?

If arginine is the direct precursor to nitric oxide, one might wonder: why not take L-arginine itself? The answer lies in bioavailability and how our bodies process these amino acids.

Arginine’s Absorption Problem: Oral L-arginine gets largely broken down by the enzyme arginase in the gut and liver before it can reach the bloodstream[6]. This first-pass metabolism means a lot of arginine never actually makes it to your blood vessels to boost NO. In other words, arginine supplements suffer from poor bioavailability – much of it is “wasted” and doesn’t deliver a big nitric oxide boost.
Citrulline’s Advantage: L-citrulline, on the other hand, is not subject to heavy breakdown in the intestines. It bypasses the arginase trap and is readily absorbed, then converted to arginine in the kidneys[7]. This efficient conversion leads to a steady increase in plasma arginine levels. In fact, studies show that L-citrulline supplementation raises blood arginine more effectively than taking arginine itself (Agarwal et al., 2017; Schwedhelm et al., 2008)[8][9]. One human trial found that half the dose of L-citrulline achieved the same blood arginine levels as a full dose of L-arginine – a testament to citrulline’s superior efficiency (Schwedhelm et al., 2008)[10]. By delivering more arginine into circulation, citrulline ultimately leads to greater nitric oxide production and stronger vasodilation effects.

The takeaway: For boosting NO, L-citrulline is the smarter choice over L-arginine. Research and expert consensus concur that arginine is simply not as reliable as citrulline for pumping up nitric oxide in vivo (Spano, as cited in Vitamin Shoppe)[11]. This is why modern pre-workouts (including all of Kaged’s line) have largely dropped arginine in favor of citrulline[12].

L-Citrulline vs. Citrulline Malate (and Other NO Boosters)

You’ve probably seen citrulline malate on many supplement labels. Citrulline malate (CM) is a compound of L-citrulline with malic acid, often in a 2:1 ratio (2 parts citrulline to 1 part malate by weight). It became popular after some early studies suggested performance benefits. However, it’s important to understand what you’re getting:

Dose and Yield: When a pre-workout claims “6 g of citrulline malate,” remember that the actual L-citrulline content is less (with a 2:1 ratio, 6 g of CM provides about 4 g of citrulline and 2g malate). Some products don’t even disclose their ratio. This means many formulas under-deliver on pure citrulline. By contrast, a product listing “10 g L-citrulline” (like Essence of Hormes) gives you the full clinical dose of the active ingredient.
Is Malate Beneficial? Malate (malic acid) is involved in the Krebs cycle (energy production), and there’s speculation it might help reduce exercise fatigue or lactic acid buildup. In theory, adding malate could aid endurance. However, most performance benefits seen in studies are attributed to the citrulline component rather than malate. In fact, a recent review noted that some citrulline malate studies failed to show benefits possibly because the actual citrulline dose was lower than expected (the tested product had closer to a 1:1 ratio, providing only half the intended citrulline dose)[13]. This suggests it’s the citrulline that really matters for NO and performance, and you need enough of it. Malate might not hurt – and could potentially help with endurance – but there’s no strong evidence that citrulline malate is superior to pure L-citrulline for boosting NO or strength training performance.
Pump and Tolerance: Anecdotally, many users find pure L-citrulline gives a better pump. Some also report that the added acid in citrulline malate can cause slight stomach discomfort at high doses[14]. This isn’t a major issue for most, but it’s worth noting. Pure L-citrulline is less acidic on the stomach.

Other nitric oxide boosters deserve a brief mention. Ingredients like beetroot juice (nitrate), agmatine sulfate, and patented compounds like Nitrosigine® (inositol-stabilized arginine silicate) are also used to increase NO or enhance pumps through various mechanisms. Nitrate from beetroot, for example, follows a different pathway (converting to NO via nitrite) and has been shown to improve endurance exercise performance in some studies. These can complement citrulline – some advanced pump formulas include multiple NO boosters. However, when comparing primary ingredients, L-citrulline stands out for its robust support in resistance exercise contexts and its ability to reliably raise arginine/NO levels. It has become the gold-standard NO booster in many pre-workouts, often dosed at 6–8 grams or more.

Bottom line: Pure L-citrulline offers the most bang for your buck in terms of actual citrulline content and NO-boosting efficacy. Citrulline malate works too (since it does provide citrulline), but you need to account for the malate portion. With a product like Essence of Hormes delivering 10 g of pure L-citrulline, you’re assured a hefty dose without any filler – the “pump with purpose” is all coming from citrulline itself.

Proven Benefits of L-Citrulline for Performance

Does L-citrulline actually translate to better workouts? According to a growing body of research, yes – especially for forms of anaerobic exercise (like weightlifting) where nitric oxide can make a difference. Here are some key performance benefits backed by clinical studies:

Greater Muscle Pumps and Vascularity: The most immediate effect users notice is a bigger pump. With the increased NO and vasodilation, muscles get engorged with blood during training. While “pump” can be subjective, studies have measured related effects. For example, in a double-blind trial, citrulline supplementation significantly increased plasma NO markers and led to enhanced blood flow signaling compared to placebo, confirming that citrulline can acutely boost the NO pathway (Schwedhelm et al., 2008)[2][8]. Many lifters value this not just for the sensation or aesthetics, but because a strong pump may correlate with better nutrient delivery and muscle performance in the session.
More Reps and Reduced Fatigue: Several studies have found that citrulline can help athletes squeeze out more repetitions before reaching exhaustion. For instance, a landmark study in 2010 showed that a single 8 g dose of citrulline malate taken 1 hour before an upper-body workout significantly increased the number of reps achieved in the later sets of a bench press exercise protocol (Perez-Guisado & Jakeman, 2010)[15]. On average, lifters were able to perform about ~1–2 extra reps on sets performed with fatigue, a roughly 18% increase in performance over placebo in that study (41 trained men)[16]. Follow-up studies by other researchers reported similar results: improved repetition performance in both upper and lower body exercises after citrulline malate supplementation (e.g. more reps on leg press, hack squat, and even bodyweight exercises like pull-ups)[17]. By buffering fatigue, citrulline allows for a higher training volume, which over time could translate to greater strength and muscle gains.
Improved Muscle Endurance: Beyond just one more rep, some evidence suggests citrulline might improve general endurance in high-intensity exercise. A study on female athletes found that citrulline malate enabled them to complete more total work across multiple sets of leg press and bench press at 80% of 1RM (Glenn et al., 2017)[18]. Other research noted small but positive effects on performance in exercises ranging from strength endurance tests to cycling sprints[19]. Not every study finds a large effect (results can vary based on dosing, timing, and the test protocol), but the trend is that citrulline especially helps in scenarios of repeated submaximal efforts or high-rep sets. In practical terms, that might mean pushing through a tough “drop set” or finishing a high-intensity interval with a bit more power.
Less Muscle Soreness: Interestingly, L-citrulline may aid in recovery by reducing delayed onset muscle soreness (DOMS). In the 2010 study above, subjects reported significantly less muscle soreness in the 24–48 hours after training when they had taken citrulline malate before the workout. Soreness ratings at 24 hours were about 40% lower with citrulline malate versus placebo, and similarly about 41% lower at 48 hours (Perez-Guisado & Jakeman, 2010)[20]. This could be due to improved blood flow helping clear metabolic waste and deliver nutrients for repair. Not all studies saw such a dramatic reduction in soreness (one later study with a different design did not replicate the effect)[21], but overall citrulline shows promise in mitigating post-exercise muscle soreness and improving recovery feelings. For athletes, that means potentially coming back stronger in the next training session.

It should be noted that citrulline is not a stimulant and doesn’t directly boost energy like caffeine. Its performance benefits are more subtle and physiological – you might notice you’re able to sustain effort longer, crank out a couple more reps, and feel less beat up afterward. Combined with other pre-workout ingredients (like caffeine for energy or beta-alanine for endurance), L-citrulline contributes an important piece of the performance puzzle: greater blood flow and endurance capacity.

Beyond the Gym: Other Benefits of L-Citrulline

L-Citrulline’s effects on nitric oxide have implications beyond just muscle pumps. Research – much of it clinical and peer-reviewed – has explored citrulline supplementation for various health and fitness outcomes. Here are a few notable benefits (with scientific backing):

Heart Health and Blood Pressure: Because NO relaxes blood vessels, L-citrulline has been studied as a natural blood pressure aid. A 2019 systematic review and meta-analysis of clinical trials concluded that citrulline supplementation can cause a moderate but significant reduction in blood pressure[22]. Specifically, across the analyzed studies, systolic blood pressure (the top number) dropped by about 4 mmHg on average in those taking L-citrulline vs. placebo[23][22]. This effect was more pronounced in trials using higher doses (≥6 g per day) and in populations with higher baseline blood pressure. A reduction of 4–5 mmHg might improve cardiovascular health outcomes, especially for people with pre-hypertension. Citrulline may thus support a healthy blood pressure and vascular function, making it more than just a gym vanity supplement. (Of course, if you have a medical condition, always consult a doctor, but this evidence underscores citrulline’s positive vascular effects.)
Erectile Dysfunction Improvement: The blood-flow boost from citrulline extends to sexual health as well. One small but notable study found that men with mild erectile dysfunction (ED) experienced improved erection hardness after supplementing with L-citrulline. In this trial, men took a placebo for one month and 1.5 g/day of L-citrulline for one month (in a crossover design). The results were striking: only 2 of 24 men (8%) saw their erection hardness score improve from “mild ED” to normal during the placebo phase, versus 12 of 24 (50%) achieving a normal erection rating after a month of L-citrulline (Cormio et al., 2011)[24][25]. In other words, citrulline significantly improved erectile function for half the participants. While citrulline isn’t as potent as prescription ED medications, the researchers noted it was safe and well-tolerated, and it could be an option for men with mild ED who prefer a natural approach. This benefit again stems from nitric oxide – the same vasodilation that pumps up your biceps can, it appears, help other muscular tissues when the situation calls for it.
Exercise Endurance (Mixed Evidence): There has been interest in whether citrulline could boost aerobic endurance (like running or cycling performance) via improved blood flow and ammonia clearance. Results here have been mixed. Some studies on cyclists and endurance athletes did not find significant improvements in time-to-exhaustion or VO₂ max from citrulline alone[26][27]. Highly trained endurance athletes may already have high baseline nitric oxide, so an NO booster might offer less benefit. However, other research has hinted at improved oxidative metabolism or slightly better high-intensity exercise tolerance with citrulline or citrulline malate. It’s an area of ongoing study. Endurance athletes might get more benefit from nitrate supplements (like beetroot), but combining those with citrulline is also being explored. For the general fitness enthusiast, the main proven gains of citrulline still lie in resistance training and high-intensity exercise rather than marathon-length efforts.
Safety and Tolerance: It’s worth mentioning that L-citrulline is generally considered very safe and well-tolerated. Doses up to 10–15 g per day have been used in studies with minimal adverse effects. Unlike some stimulant ingredients, citrulline won’t raise heart rate or blood pressure (in fact, it tends to lower BP). The most common side effect, if any, is mild GI discomfort at high doses, but pure L-citrulline tends to cause fewer issues than acidic citrulline malate[14]. Overall, for healthy individuals, citrulline is a low-risk supplement. Of course, as with any supplement, you should stick to recommended dosages and quality products.

Dosage: Why 10 Grams of Citrulline?

Clinical studies and expert reviews suggest that effective doses of L-citrulline for performance are typically in the range of about 6 to 8 grams taken 30–60 minutes before exercise[28][29]. This is why you’ll often see 6–8 g per serving in many pre-workout products. So what’s the idea behind the 10 g of pure L-citrulline in Essence of Hormes?

Fully “Saturated” Dose: Ten grams is at the upper end of what’s used, intended to ensure you’re fully saturating the pathways that boost NO. If 6–8 g is good, 10 g may provide a bit more arginine conversion and possibly a longer-lasting pump. It essentially guarantees you’re not falling short. Remember, some of the citrulline in supplements will be used to convert to arginine and then NO, and beyond a certain point excess might just be excreted. But going slightly above the typical dose can act as insurance that you achieve peak blood levels. Importantly, 10 g of pure L-citrulline is roughly equivalent to what would have been 15–16 g of citrulline malate 2:1 (since that would contain ~10 g citrulline). Hardly any pre-workouts use that much due to cost – making 10 g pure a standout dose.
Clinical Justification: While 8 g of citrulline malate (≈5.6 g citrulline) has shown benefits, some studies that used higher doses did observe trends of improvement. For example, a study using 9 g/day of citrulline in hypertensive adults found significant blood pressure reductions[30]. Another using 12 g of citrulline malate in athletes still found it to be safe (though it didn’t significantly enhance sprint performance)[31]. These data indicate that doses up to 10 g are not only safe but might be advantageous in certain outcomes. Essentially, 10 g aligns with the highest “full doses” used in practice for maximizing the pump and performance effect.
No Fillers Needed: The choice to use 10 g in a product like Essence of Hormes is also about providing a clinically dosed formula – delivering what the label promises. It stands in contrast to some pre-workouts that use, say, 4 g of citrulline and rely on malate or other cheap additions. Here, you’re getting the real deal at a level used in research. The manufacturers are framing it as a “pump with purpose” – not just for show, but to potentially improve your workout quality in a meaningful way.

For most people, taking 10 g citrulline about 30 minutes before training (perhaps split into two 5 g scoops if desired) will yield excellent results. Start a bit lower if you’re new to it, but know that this ingredient is very forgiving. And unlike certain stimulants or creatine, you don’t need to load citrulline or take it every day – it works acutely, so you can take it only on training days if you prefer.

Citrulline Content in Popular Pre-Workouts

To put the 10 g of L-citrulline in perspective, let’s compare the citrulline content of some other popular pre-workout supplements on the market. This can help illustrate how fully dosed Essence of Hormes is relative to others:

Pre-Workout Product	Citrulline Content per Serving
Essence of Hormes	10 g L-Citrulline (pure form, fully dosed)
Gorilla Mode Pre-Workout	10 g L-Citrulline (per 2-scoop serving)
Legion Pulse Pre-Workout	8 g Citrulline Malate (2:1) ≈ 5.3 g actual L-citrulline
Redcon1 Total War	6 g Citrulline Malate (2:1) ≈ 4 g actual L-citrulline
JYM Supplement Science Pre JYM	6 g Citrulline Malate (2:1) ≈ 4 g actual L-citrulline
Bucked Up Pre-Workout	6 g Citrulline Malate (2:1) ≈ 4 g actual L-citrulline
Kaged Muscle Pre-Kaged	6.5 g L-Citrulline (fermented pure citrulline)
Ghost Legend Pre-Workout	4 g L-Citrulline (pure)
Optimum Nutrition Gold Std. Advanced	6 g L-Citrulline (in the new “Advanced” version)
Optimum Nutrition Gold Std. (original)	0.75 g L-Citrulline (in older formula)

(Note: “Citrulline malate” entries are given with approximate L-citrulline yield in italics. Many proprietary blends use citrulline malate without clarifying the ratio; we assumed a common 2:1 ratio for comparison. Pure L-citrulline is listed directly.)

As you can see, 10 grams of pure L-citrulline in a single serving is virtually unheard of outside of a few hardcore products (Gorilla Mode only reaches 10 g if you take the max 2 scoops). Most mainstream pre-workouts give you around 4 to 6 grams of citrulline (often as citrulline malate, meaning you might only get 3–4 g of actual citrulline). Even some “clinically dosed” products stop at ~6–8 g. Essence of Hormes, by providing the full 10 g, is aiming to be top-shelf in delivering the ultimate pump dose.

For users, this means if you switch from a pre-workout with say 4–6 g citrulline up to one with 10 g, you can expect a noticeably bigger pump and potentially better performance effects – assuming all else (training, diet, rest) is equal. It’s the difference between a good dose and a truly maxed-out dose.

Conclusion

L-Citrulline is much more than just a “pump” ingredient to make your muscles look bigger in the mirror (though it certainly does that!). By elevating nitric oxide, citrulline improves blood flow in a way that can enhance your workout performance – allowing you to train harder and recover faster. Scientific studies support its ability to increase training volume (more reps), decrease post-workout muscle soreness, and even contribute to cardiovascular and sexual health by improving circulation. It outperforms the older NO booster L-arginine due to better absorption, and when dosed adequately it provides reliable benefits without significant side effects.

The 10 g of pure L-citrulline in Essence of Hormes is a “pump with purpose” – not only delivering sleeve-splitting vascularity in the gym, but doing so at a dose rooted in what research suggests is effective. In a market where some supplements under-dose key ingredients, it’s refreshing to see a product err on the side of giving you more of the good stuff. When combined with a solid training program, a well-rounded diet, and other supportive ingredients (like caffeine, beta-alanine, creatine, etc., also present in Essence of Hormes), citrulline can be a powerful ally in your fitness journey.

TL;DR: L-Citrulline helps you lift more, look more pumped, and potentially even live healthier by fueling your body’s nitric oxide system. So the next time you crush a workout and marvel at the pump, you’ll know it’s not just broscience – it’s real science working hard under your skin, and citrulline is one of the key drivers behind it. Pump with purpose, and let science fuel your gains!

Works Cited (Research and Studies):

Schwedhelm, E. et al. (2008). Pharmacokinetic and pharmacodynamic properties of oral L-citrulline and L-arginine: impact on nitric oxide metabolism. British Journal of Clinical Pharmacology, 65(1), 51–59[32]. (Demonstrated that oral L-citrulline elevated plasma arginine and NO levels more efficiently than oral arginine.)
Pérez-Guisado, J. & Jakeman, P. (2010). Citrulline malate enhances athletic anaerobic performance and relieves muscle soreness. Journal of Strength and Conditioning Research, 24(5), 1215–1222. doi:10.1519/JSC.0b013e3181cb28e0[20][15]. (Found 8 g citrulline malate pre-workout increased bench press repetitions and significantly reduced muscle soreness in the days after exercise.)
Barkhidarian, B. et al. (2019). Effects of L-citrulline supplementation on blood pressure: A systematic review and meta-analysis. Avicenna Journal of Phytomedicine, 9(1), 10–20[33]. (Meta-analysis of 8 RCTs; concluded citrulline supplementation significantly lowers systolic blood pressure by ~4 mmHg on average, with higher doses ≥6 g/day also reducing diastolic BP.)
Cormio, L. et al. (2011). Oral L-citrulline supplementation improves erection hardness in men with mild erectile dysfunction. Urology, 77(1), 119–122[34]. (Single-blind trial showing 1.5 g/day citrulline for 1 month improved erectile function in 50% of men with mild ED vs 8% on placebo, indicating enhanced blood flow and hardness.)
Wax, B. et al. (2015 & 2016). (Series of studies on citrulline malate) – e.g., Wax, B. et al. 2015 in Journal of Strength & Conditioning Research; Wax, B. et al. 2016 in Journal of Dietary Supplements. (Reported that 8 g citrulline malate improved performance in lower-body weight exercises and upper-body bodyweight exercises, respectively, albeit with modest effect sizes[17].)
Glenn, J.M. et al. (2017). Acute citrulline malate supplementation improves upper- and lower-body submaximal weightlifting performance in resistance-trained females. Journal of Dietary Supplements, 14(3), 269–282. doi:10.1080/19390211.2016.1207585. (Showed enhanced volume performance in women doing multiple sets of leg press and bench press at 80% 1RM after 8 g citrulline malate[18].)

(Additional references and source links are provided above in the text via in-text citations. All cited studies are peer-reviewed. Always consult the original research for full details.)

[1] [3] [4] [5] [6] [7] [8] [12] [28] Why L-Citrulline is More Effective Than L-Arginine