Xi Gua
StarCitrullus lanatus (Thunb.) Matsum. et Nakai
Traditionally used for
- Colds & fever
- Urinary & fluids
- Mood & calm
- Liver & jaundice
☯ TCM Properties
Clears Summer-Heat; Generates Fluids and Relieves Thirst; Eliminates Irritability; Promotes Urination; Clears Damp-Heat and Resolves Jaundice
Traditional Chinese Uses
Xi Gua (watermelon fruit and rind) is a cold, sweet herb used in Chinese medicine to clear Summerheat, quench thirst, relieve urinary irritation, and cool the body during hot weather. As one of the most cooling foods in Chinese dietary medicine, it is consumed widely in summer for its cooling, diuretic, and thirst-quenching properties. In TCM, even the rind (Xi Gua Pi) and the green outer layer are used separately for their clearing and diuretic effects. Moderate consumption supports recovery from febrile conditions and helps prevent heat-stroke.
Western Herbalism Properties
Relationships
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Botanical Description
Citrullus lanatus is a trailing or climbing annual vine in the Cucurbitaceae family, native to Africa and widely cultivated in warm regions worldwide. The stems are hairy, branched, and bear tendrils that allow the plant to climb or sprawl across the ground. Leaves are deeply pinnately lobed, grey-green, and roughly hairy, measuring 5-20 cm long. The plant produces monoecious yellow flowers approximately 3 cm across. The fruit is a large pepo with a smooth green rind, often striped or mottled, and juicy red, pink, or yellow flesh containing numerous flat, oval seeds that may be black, brown, or white. In TCM, the fruit (Xi Gua) is regarded as cooling, and the rind and seeds are also used medicinally.
Active Constituents
L-Citrulline
Non-protein amino acidConcentration: 3.9 to 28.5 mg/g dry weight depending on cultivar; rind 24.7 and flesh 16.7 mg/g dry weight, which inverts to about 1.3 and 1.9 mg/g on a fresh weight basis
The amino acid the genus is named for and the constituent behind almost all modern interest in the fruit. Citrulline is converted to arginine and feeds the nitric oxide pathway. Red-fleshed cultivars contain notably less than yellow or orange-fleshed ones (7.4 against 28.5 and 14.2 mg/g dry weight), so the citrulline content of an ordinary red watermelon is at the bottom of the published range.
L-Arginine
Amino acidPresent in the flesh and generated endogenously from ingested citrulline. In a four-week randomised trial, watermelon flesh at 152 or 304 g/day significantly raised plasma L-arginine and the L-arginine to ADMA ratio compared with control even though blood pressure and plasma nitric oxide did not change.
Lycopene
Acyclic carotenoidThe pigment of red-fleshed watermelon. Serum lycopene rises measurably with watermelon juice intake, which confirms absorption, but in the trials where lycopene rose significantly the vascular endpoints did not, so raised circulating lycopene has not translated into a demonstrated vascular effect from watermelon.
⚠ Drug Interactions
Antihypertensive drugs
The mechanistic argument is that watermelon citrulline raises arginine availability for nitric oxide synthesis and so promotes vasodilation. The trial evidence does not support a clinically meaningful effect from eating watermelon. A four-week randomised placebo-controlled trial in 39 adults with elevated blood pressure found no significant difference in 24 h ambulatory blood pressure at either 152 or 304 g/day against control, and a 2025 meta-analysis found that watermelon intake, unlike isolated L-citrulline supplementation, did not significantly improve pulse wave velocity or flow-mediated dilation in middle-aged and older adults. A larger meta-analysis did find a pulse wave velocity improvement of 0.9 m/s with longer-term watermelon consumption, so the literature is not unanimous, but no trial has shown a blood pressure fall large enough to matter alongside drug therapy.
Clinical note: No dose adjustment or monitoring is warranted for ordinary dietary watermelon. Concentrated L-citrulline supplements are a different matter and should not be equated with the fruit.
Phosphodiesterase type 5 inhibitors (sildenafil, tadalafil)
Both act on the nitric oxide and cyclic GMP pathway, sildenafil by blocking cGMP breakdown and watermelon citrulline by supplying substrate upstream of nitric oxide synthase, which is the basis of the popular claim that watermelon is a natural PDE5 alternative. No trial has tested the combination, and the trials of watermelon alone show no significant change in plasma nitric oxide or blood pressure at 152 to 304 g/day, so there is no measured effect for the drug to add to.
Clinical note: Recorded to answer the question rather than to restrict the food. Watermelon is not a substitute for a PDE5 inhibitor and there is no reason to avoid eating it on one.
Evidence Tier
Strong evidence · 5 studiesRecorded studies by study design, strongest design at the top. This is a study-design tier only, not a GRADE rating: it does not weigh risk of bias, consistency or precision.
Systematic review / meta-analysis
2
0 verified · 2 unverified
Show 2 studies
- Effects of l-citrulline supplementation and watermelon consumption on longer-term and postprandial vascular function and cardiometabolic risk markers: a meta-analysis of randomised controlled trials in adults
- Effects of L-citrulline supplementation and watermelon intake on arterial stiffness and endothelial function in middle-aged and older adults: a systematic review and meta-analysis of randomized controlled trials
Randomized controlled trial
3
0 verified · 3 unverified
Show 3 studies
- Dose–Response Effect of Watermelon Consumption on Ambulatory Blood Pressure in Adults with Elevated Blood Pressure: A Randomized Controlled Pilot Trial
- Daily 100% watermelon juice consumption and vascular function among postmenopausal women: A randomized controlled trial
- Supplemental Watermelon Juice Attenuates Acute Hyperglycemia-Induced Macro-and Microvascular Dysfunction in Healthy Adults
Other clinical trial
0
Observational / case report
0
In vitro / animal
0
Other / unclassified
0
Verified: design read from PubMed for a DOI that resolves to the cited paper Unverified: taken from the study's recorded description
Clinical Studies
Dose–Response Effect of Watermelon Consumption on Ambulatory Blood Pressure in Adults with Elevated Blood Pressure: A Randomized Controlled Pilot Trial
Thirty-nine adults with elevated blood pressure were randomised for four weeks to control, 152 g/day or 304 g/day of watermelon flesh. Mean 24 h ambulatory blood pressure did not differ significantly between groups (130.2, 130.0 and 124.9 mm Hg), and there were no significant changes in fasting glucose, insulin, lipids or nitric oxide. Plasma L-arginine and the L-arginine to ADMA ratio did increase significantly in the watermelon groups after adjustment for age, BMI, race and gender.
Effects of l-citrulline supplementation and watermelon consumption on longer-term and postprandial vascular function and cardiometabolic risk markers: a meta-analysis of randomised controlled trials in adults
Seventeen randomised controlled trials of L-citrulline and ten of watermelon were pooled. Longer-term watermelon consumption improved pulse wave velocity by 0.9 m/s and postprandial glucose fell by 0.6 mmol/L after watermelon, while longer-term L-citrulline supplementation improved flow-mediated dilation by 0.9 percentage points. No postprandial effects on vascular function markers were found, and effects of watermelon on flow-mediated dilation were not studied.
Effects of L-citrulline supplementation and watermelon intake on arterial stiffness and endothelial function in middle-aged and older adults: a systematic review and meta-analysis of randomized controlled trials
Eight randomised controlled trials with 176 participants were pooled. L-citrulline supplementation significantly improved flow-mediated dilation (1.81, 95 percent CI 0.76 to 2.85) and reduced brachial-ankle pulse wave velocity in subgroup analysis, but watermelon supplementation did not significantly improve either pulse wave velocity or flow-mediated dilation in middle-aged and older adults. The authors note the watermelon literature is thin.
Daily 100% watermelon juice consumption and vascular function among postmenopausal women: A randomized controlled trial
Twenty-one healthy postmenopausal women took two 360 mL servings of 100 percent watermelon juice or isocaloric placebo daily for four weeks in a double-blind crossover design with a two-week washout. Circulating lycopene rose significantly but arginine, citrulline, pulse pressure, pulse wave velocity, 24 h ambulatory blood pressure and flow-mediated dilation were all unchanged. Fasting serum glucose rose slightly but not to a clinically significant degree.
Supplemental Watermelon Juice Attenuates Acute Hyperglycemia-Induced Macro-and Microvascular Dysfunction in Healthy Adults
Seventeen healthy young adults took 500 mL of watermelon juice or calorie-matched placebo daily for two weeks in a double-blind crossover trial, then underwent an oral glucose tolerance test. Postprandial flow-mediated dilation area under the curve was higher after watermelon juice (838 against 539 percent times 90 min) as was microvascular blood flow, and baseline tissue oxygen saturation rose from 65.9 to 71.2 percent. This is the clearest positive watermelon result, obtained under an induced hyperglycaemic challenge rather than at rest.
Historical Texts
Ri Yong Ben Cao
Yuan dynastyBen Cao Gang Mu
Ming dynastyReferences
- Rimando AM, Perkins-Veazie PM. Determination of citrulline in watermelon rind . Journal of Chromatography A (2005) [DOI]
- Burton-Freeman B, Freeman M, Zhang X, Sandhu A, Edirisinghe I. Watermelon and l-Citrulline in Cardio-Metabolic Health: Review of the Evidence 2000–2020 . Current Atherosclerosis Reports (2021) [DOI]
This information is for educational purposes only and is not intended to replace professional medical advice. Always consult a qualified healthcare provider before using any herbal remedy, especially if you are pregnant, nursing, or taking medications.
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