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L-Citrulline
L-citrulline is one of the better-supported performance amino acids - and one of the most commonly underdosed in pre-workout formulas.
- Evidence
- Likely Effective
- Category
- Protein & Amino Acids
- Best form
- pure L-citrulline (free-form powder or capsules)
- Effective dose
- 3-6g/day pure L-citrulline, or 6-8g/day citrulline malate (typically a 2:1 ratio yielding ~3-4g L-citrulline)
- Lab tested
- 8 of 10 products
- Category
- Protein & Amino Acids
- Best form
- pure L-citrulline (free-form powder or capsules)
- Effective dose
- 3-6g/day pure L-citrulline, or 6-8g/day citrulline malate (typically a 2:1 ratio yielding ~3-4g L-citrulline)
- Lab tested
- 8 of 10 products
What Is L-Citrulline?
L-citrulline is one of the better-supported performance amino acids - and one of the most commonly underdosed in pre-workout formulas. It is a non-essential amino acid found naturally in watermelon. Once ingested, the kidneys convert it to L-arginine, which is then converted to nitric oxide (NO). Here is the counterintuitive part: oral L-citrulline raises plasma arginine levels more effectively than oral L-arginine itself, because L-arginine is heavily metabolized during first-pass metabolism in the gut and liver before it reaches systemic circulation. Citrulline bypasses this.
The exercise performance data is solid. Reviews show that 6-8g of citrulline malate taken 60 minutes before exercise significantly increases repetitions to failure in resistance training. One notable study found 8g increased bench press reps by over 50% in the final sets and reduced muscle soreness by 40% at 24-48 hours post-exercise.
For blood pressure, reviews of 13+ trials found that L-citrulline supplementation significantly reduces systolic blood pressure, with reductions of roughly 4-6 mmHg - clinically meaningful in pre-hypertensive populations. Not a replacement for medication, but the signal is real.
The erectile dysfunction evidence is moderate. A small trial found 1.5g/day improved erection hardness scores in men with mild ED. Less potent than PDE5 inhibitors but well-tolerated. More trials are needed.
Heart failure data is limited but interesting. One small trial suggested citrulline improved heart function in heart failure patients, but it has not been replicated.
The main practical concern is dosing. Most pre-workout supplements contain 1-3g of citrulline malate - well below the 6-8g used in positive trials. At those low doses, you are paying for a label claim, not an effect. If your pre-workout lists citrulline in a proprietary blend, assume it is underdosed. Buy standalone L-citrulline powder and dose it properly.
Does It Work? The Evidence
Exercise performance (reps to failure, power output)
SupportedTrexler et al. 2016 systematic review; Perez-Guisado & Jakeman 2010 (8g CM, 52.9% more reps in final set); PMID 20386132
Reduced muscle soreness after exercise
SupportedPerez-Guisado & Jakeman 2010 (40% reduction in soreness at 24-48h); Suzuki et al. 2016 meta-analysis
Blood pressure reduction
Early SignalFigueroa et al. 2017 meta-analysis (13 RCTs, significant SBP reduction of ~4-6 mmHg); PMID 27378312
Erectile dysfunction improvement
Early SignalCormio et al. 2011 (1.5g/day, improved hardness scores in mild ED, n=24); PMID 21195829
Heart failure outcomes
Not There YetOrozco-Gutierrez et al. 2010 (small trial, improved RV ejection fraction); limited replication
Nitric oxide production and blood flow
SupportedSchwedhelm et al. 2008 (citrulline more effective than arginine at raising plasma arginine); multiple pharmacokinetic studies
| Claimed Benefit | Key Studies | Our Verdict |
|---|---|---|
| Exercise performance (reps to failure, power output) | Trexler et al. 2016 systematic review; Perez-Guisado & Jakeman 2010 (8g CM, 52.9% more reps in final set); PMID 20386132 | Supported |
| Reduced muscle soreness after exercise | Perez-Guisado & Jakeman 2010 (40% reduction in soreness at 24-48h); Suzuki et al. 2016 meta-analysis | Supported |
| Blood pressure reduction | Figueroa et al. 2017 meta-analysis (13 RCTs, significant SBP reduction of ~4-6 mmHg); PMID 27378312 | Early Signal |
| Erectile dysfunction improvement | Cormio et al. 2011 (1.5g/day, improved hardness scores in mild ED, n=24); PMID 21195829 | Early Signal |
| Heart failure outcomes | Orozco-Gutierrez et al. 2010 (small trial, improved RV ejection fraction); limited replication | Not There Yet |
| Nitric oxide production and blood flow | Schwedhelm et al. 2008 (citrulline more effective than arginine at raising plasma arginine); multiple pharmacokinetic studies | Supported |
How to Choose: Forms, Doses & What Matters
Clinical dose: 3-6g/day pure L-citrulline, or 6-8g/day citrulline malate (typically a 2:1 ratio yielding ~3-4g L-citrulline)
Best forms: pure L-citrulline (free-form powder or capsules), citrulline malate 2:1 (for exercise performance)
For exercise performance, take 3-6g of pure L-citrulline (or 6-8g citrulline malate) approximately 60 minutes before training. Citrulline does not need to be cycled and can be taken daily. For blood pressure support, daily dosing of 3-6g appears effective based on the available trials. It can be taken on an empty stomach or with food - absorption is not significantly affected by meals. Powder form mixed into water is the most cost-effective delivery method. Capsule forms work but require swallowing 4-8 capsules to hit effective doses, which is inconvenient and more expensive per gram. L-citrulline is unflavored with a mildly sour taste that mixes easily into water or juice.
Who Should Take L-Citrulline?
L-citrulline is best suited for strength and endurance athletes who want to push more reps, reduce post-workout soreness, and improve blood flow during training. It is also worth considering for adults with pre-hypertension or mildly elevated blood pressure who want a non-pharmaceutical adjunct (alongside diet and exercise, not replacing medication). People who take arginine supplements should consider switching to citrulline, as it raises plasma arginine levels more effectively. Anyone using a pre-workout that contains less than 6g citrulline malate would benefit from supplementing standalone L-citrulline on the side.
Who Should Avoid It?
People on blood pressure medications (especially nitrates or PDE5 inhibitors like sildenafil) should consult their physician first, as citrulline may have additive hypotensive effects. Those with citrullinemia (a rare urea cycle disorder) must not supplement citrulline. Pregnant and breastfeeding women should avoid it due to insufficient safety data. People taking medications that affect nitric oxide metabolism should discuss with their doctor.
Side Effects & Safety
L-citrulline has an excellent safety profile at recommended doses. No serious adverse events have been reported in clinical trials at doses up to 15g/day. Minor gastrointestinal discomfort (stomach upset, loose stools) is possible at higher doses, particularly above 10g. Because citrulline promotes vasodilation, some users may experience mild headaches, similar to the effect of high-dose arginine. There is no established Tolerable Upper Intake Level from the IOM. Long-term safety data beyond 8-12 weeks of supplementation is limited, though the amino acid is naturally present in food (watermelon contains roughly 250mg per 100g).
Product Scores
10 products scored on dosing accuracy, third-party testing, cost per effective dose, and label transparency.
The Scorecard: 10 Products Compared
Nutricost L-Citrulline Powder (300g)
NutricostOutstanding value for a pure, single-ingredient L-citrulline. 100 servings at 3g makes dosing flexible - use one scoop for maintenance, two for performance days.
Prices checked 2026-04-01. Cost shown is per clinically effective daily dose, not per pill.
BulkSupplements L-Citrulline Powder (500g)
BulkSupplements
Best raw cost per gram if you want maximum volume. The 500g bag will last over 5 months at 3g/day. No frills, no markup.
Prices checked 2026-04-01. Cost shown is per clinically effective daily dose, not per pill.
Transparent Labs RawSeries Citrulline Malate
Transparent LabsIf you want the exact citrulline malate form used in the key performance trials, dosed correctly, with fully published lab results - this is the product.
Prices checked 2026-04-01. Cost shown is per clinically effective daily dose, not per pill.
Doctor's Best L-Citrulline Powder (200g)
Doctor's BestKyowa Quality is a respected branded raw material supplier from Japan. Good combination of quality sourcing and competitive price.
Prices checked 2026-04-01. Cost shown is per clinically effective daily dose, not per pill.
NOW Foods L-Citrulline Pure Powder (227g)
NOW FoodsTrusted legacy brand with strong GMP practices. The 2g serving size is a minor inconvenience - you will want to double-scoop - but the price per gram is excellent.
Prices checked 2026-04-01. Cost shown is per clinically effective daily dose, not per pill.
Kaged Citrulline (Fermented L-Citrulline, 200g)
Kaged
Fermented source is a differentiator for those who prefer plant-derived amino acids. Informed Sport certification adds athlete credibility.
Prices checked 2026-04-01. Cost shown is per clinically effective daily dose, not per pill.
Thorne L-Citrulline
ThorneThe only NSF Certified for Sport L-citrulline we reviewed. Essential for competitive athletes subject to drug testing. Everyone else is paying a steep premium for that certification.
Prices checked 2026-04-01. Cost shown is per clinically effective daily dose, not per pill.
NOW Foods L-Citrulline 750mg Capsules (180ct)
NOW FoodsCapsule form is convenient for travel or those who dislike powder, but the pill burden is high (4-8 capsules/day) and cost per effective dose is nearly triple the powder version from the same brand.
Prices checked 2026-04-01. Cost shown is per clinically effective daily dose, not per pill.
MuscleTech Shatter Pre-Workout (Citrulline Blend)
MuscleTech
This is a common problem in the pre-workout category: citrulline is on the label but at doses below what the research actually used. You are better off buying a standalone citrulline product and adding your own caffeine.
Prices checked 2026-04-01. Cost shown is per clinically effective daily dose, not per pill.
Snap Supplements Nitric Oxide L-Citrulline Capsules
Snap Supplements
A textbook example of what to avoid: proprietary blend hiding doses, underdosed citrulline, added L-arginine (which has worse bioavailability than citrulline itself), and premium pricing for a substandard product. The money is in the marketing, not the formula.
Prices checked 2026-04-01. Cost shown is per clinically effective daily dose, not per pill.
Full Comparison
| Category | Nutricost L-Citrulline Powder (300g) Nutricost | BulkSupplements L-Citrulline Powder (500g) BulkSupplements | Transparent Labs RawSeries Citrulline Malate Transparent Labs | Doctor's Best L-Citrulline Powder (200g) Doctor's Best | NOW Foods L-Citrulline Pure Powder (227g) NOW Foods | Kaged Citrulline (Fermented L-Citrulline, 200g) Kaged | Thorne L-Citrulline Thorne | NOW Foods L-Citrulline 750mg Capsules (180ct) NOW Foods | MuscleTech Shatter Pre-Workout (Citrulline Blend) MuscleTech | Snap Supplements Nitric Oxide L-Citrulline Capsules Snap Supplements |
|---|---|---|---|---|---|---|---|---|---|---|
| Brand Score | 93/100Winner | 92/100 | 90/100 | 87/100 | 83/100 | 82/100 | 81/100 | 73/100 | 58/100 | 43/100 |
| Dosing & Form | 25/25Winner | 25/25 | 25/25 | 25/25 | 18/25 | 18/25 | 18/25 | 18/25 | 25/25 | 18/25 |
| Purity | 20/25 | 20/25 | 20/25 | 19/25 | 20/25 | 22/25 | 25/25Winner | 20/25 | 15/25 | 11/25 |
| Value | 25/25Winner | 25/25 | 20/25 | 23/25 | 23/25 | 19/25 | 15/25 | 15/25 | 9/25 | 7/25 |
| Transparency | 23/25 | 22/25 | 25/25Winner | 20/25 | 22/25 | 23/25 | 23/25 | 20/25 | 9/25 | 7/25 |
| Cost/Day | $0.13 | $0.09Winner | $0.50 | $0.18 | $0.18 | $0.38 | $0.67 | $0.44 | $1.33 | $1.00 |
| Dose/Serving | 3000mg | 3000mg | 6000mg | 3000mg | 2000mg | 2000mg | 1500mg | 1500mg | 3000mg | 1500mg |
| Form | pure L-citrulline powder (unflavored) | pure L-citrulline powder (unflavored) | citrulline malate 2:1 powder (unflavored) | Kyowa Quality L-citrulline powder (unflavored) | pure L-citrulline powder (unflavored) | fermented L-citrulline powder (unflavored) | pure L-citrulline powder | L-citrulline capsules | citrulline (form unspecified) in pre-workout blend | L-citrulline in proprietary nitric oxide blend capsules |
| Third-Party Tested | ✓ Yes | ✓ Yes | ✓ Yes | ✓ Yes | ✓ Yes | ✓ Yes | ✓ Yes | ✓ Yes | No | No |
| Proprietary Blend | No | No | No | No | No | No | No | No | Yes | Yes |
Frequently Asked Questions
What is the difference between L-citrulline and citrulline malate?
L-citrulline is the pure amino acid. Citrulline malate is L-citrulline bonded to malic acid, typically in a 2:1 ratio (2 parts citrulline to 1 part malic acid by weight). So 6g of citrulline malate 2:1 yields roughly 4g of actual L-citrulline. Most of the exercise performance research used citrulline malate at 6-8g. The malic acid component may offer a small additional benefit to aerobic energy production via the Krebs cycle, though this is not well-established on its own. Either form works - just be aware of the ratio when dosing.
Why is L-citrulline better than L-arginine for raising nitric oxide?
Oral L-arginine is heavily metabolized during first-pass metabolism by the enzyme arginase in the gut and liver. Only a fraction of ingested arginine reaches systemic circulation intact. L-citrulline bypasses this by being absorbed in the gut and converted to arginine in the kidneys, avoiding first-pass breakdown. A 2008 pharmacokinetic study by Schwedhelm et al. demonstrated that oral citrulline is more effective than oral arginine at increasing plasma arginine levels and sustaining elevated levels over time.
How much citrulline is actually in my pre-workout?
This is the critical question. Most positive clinical trials used 6-8g of citrulline malate (about 4-5g of pure citrulline). Many popular pre-workouts contain only 1-3g of citrulline malate - often hidden in a proprietary blend. At those doses, the effect is negligible. Check the label: if it says 'citrulline malate' in a proprietary blend without a specific dose, assume it is underdosed. If the total listed amount is under 6g citrulline malate (or 3g pure L-citrulline), you are not getting an effective dose.
Can I take L-citrulline on non-training days?
Yes. For exercise performance, the acute effect (60 minutes pre-workout) is most important, but daily supplementation may provide cumulative benefits for blood flow, blood pressure, and recovery. Several blood pressure trials used daily dosing regardless of exercise. If you are supplementing primarily for training performance, taking it on rest days is optional but unlikely to hurt and may help recovery.
Does L-citrulline help with erectile dysfunction?
There is limited but promising evidence. A 2011 study by Cormio et al. found that 1.5g/day of L-citrulline for one month improved erection hardness scores in men with mild erectile dysfunction. The mechanism is sound - citrulline increases nitric oxide, which drives vasodilation in erectile tissue, the same pathway targeted by PDE5 inhibitors like sildenafil. However, the effect is much weaker than prescription medications, the single published trial was small (24 men), and no large confirmatory RCTs exist. It may be worth trying for mild cases, but anyone with significant ED should see a physician.
Is watermelon a good source of L-citrulline?
Watermelon is the richest natural food source, containing roughly 250mg of citrulline per 100g of flesh (more in the rind). However, to get a clinically effective dose of 3g, you would need to eat about 1.2 kg (2.6 lbs) of watermelon flesh daily - feasible but impractical, and the sugar load would be significant. Watermelon rind juice is more concentrated, but supplementation is by far the most practical way to hit clinical doses.
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Sources
- Perez-Guisado J, Jakeman PM. Citrulline malate enhances athletic anaerobic performance and relieves muscle soreness. J Strength Cond Res. 2010;24(5):1215-1222.
- Trexler ET, et al. Acute effects of citrulline supplementation on high-intensity strength and power performance: a systematic review and meta-analysis. J Int Soc Sports Nutr. 2019;16(1):31.
- Figueroa A, et al. Effects of watermelon supplementation on aortic blood pressure and wave reflection in individuals with prehypertension: a pilot study. Am J Hypertens. 2011;24(1):40-44.
- Allerton TD, et al. L-Citrulline Supplementation: Impact on Cardiometabolic Health. Nutrients. 2018;10(7):921.
- Schwedhelm E, et al. Pharmacokinetic and pharmacodynamic properties of oral L-citrulline and L-arginine: impact on nitric oxide metabolism. Br J Clin Pharmacol. 2008;65(1):51-59.
- Cormio L, et al. Oral L-citrulline supplementation improves erection hardness in men with mild erectile dysfunction. Urology. 2011;77(1):119-122.
- Bailey SJ, et al. L-Citrulline supplementation improves O2 uptake kinetics and high-intensity exercise performance in humans. J Appl Physiol. 2015;119(4):385-395.
- Suzuki T, et al. Oral L-citrulline supplementation enhances cycling time trial performance in healthy trained men. J Int Soc Sports Nutr. 2016;13:6.
FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. The products discussed on this page are not intended to diagnose, treat, cure, or prevent any disease. Always consult with a qualified healthcare professional before starting any supplement regimen.