Why take citrulline instead of arginine?

Oral arginine is largely broken down before it reaches the bloodstream. Citrulline bypasses that and is converted to arginine in the kidney, producing higher plasma arginine from a smaller dose.

How much should I take?

Vascular trials typically used 3 to 6 g of L-citrulline daily, sometimes split into two doses.

Is citrulline malate the same thing?

No. Citrulline malate is dosed higher for exercise performance and contains malate, so it delivers less citrulline per gram.

How much will it lower my blood pressure?

Modestly, typically a few millimetres of mercury in trials. It is not a substitute for antihypertensive treatment.

How long until it does anything?

Plasma arginine rises within hours, but vascular measures in trials were assessed over 4 to 12 weeks.

Anyone on nitrate medication or PDE5 inhibitors, and anyone with significant kidney disease, without medical advice.

Outcome

Strong Evidence

Effectiveness 4/5

L-Citrulline for Endothelial Function

Citrulline raises plasma arginine more effectively than arginine itself, and measurably improves flow-mediated dilation.

Overview

Verdict

Strong yes

L-citrulline raises plasma arginine more effectively than oral arginine and has been associated with modest improvements in flow-mediated dilation and blood pressure, most clearly in people with existing endothelial impairment.

How It Works

Downstream effects

Converted to arginine in the kidney, bypassing first-pass arginase

Raises plasma arginine more than oral arginine at equal doses

Increases substrate for endothelial nitric oxide synthase

Nitric oxide raises cyclic GMP and relaxes vascular smooth muscle

Reduces platelet aggregation and leukocyte adhesion

Also inhibits arginase, preserving the arginine pool

Dosing & Protocol

Doses used in human trials

Purpose	Dose	Schedule	Notes
Vascular and blood pressure studies	3-6 g L-citrulline	Once daily	The most common range in endothelial trials
Citrulline malate for performance	6-8 g	60-90 minutes before exercise	Roughly 1.1 g of malate per 1 g citrulline in a 1:1 ratio
Sustained vascular use	1.5 g	Twice daily	Splitting maintains steadier plasma arginine
Higher-dose research protocols	up to 10 g	Once daily	Digestive upset becomes more common

Effects on vascular measures build over weeks. Single doses raise plasma arginine but do not remodel endothelial function.

Simple protocol

1
Choose plain L-citrulline for vascular goals
Citrulline malate is dosed for exercise performance and delivers less citrulline per gram.
2
Take 3-6 g daily· 8-12 weeks
Consistency matters more than timing for endothelial outcomes.
3
Split the dose if your stomach objects
1.5 g twice daily is better tolerated and keeps arginine levels steadier.
4
Do not treat it as blood pressure therapy
Effects are modest. Keep prescribed antihypertensives and monitoring in place.
5
Address the bigger levers
Smoking, blood pressure control, exercise and lipid management move endothelial function far more.
6
Reassess at 12 weeks
Blood pressure readings are the practical marker most people can track.

Evidence

Best-established finding: Raises plasma arginine more than equivalent oral arginine
Vascular outcomes: Modest improvement in flow-mediated dilation and blood pressure
Typical dose: 3-6 g daily
Trial duration: Mostly 4-12 weeks
Who benefits most: Adults with existing endothelial impairment
Main limitation: Small short trials; blood pressure effects are a few mmHg at most

Safety

Do not combine with nitrate medication

Citrulline works through nitric oxide. Taken with nitrates or PDE5 inhibitors it can cause an excessive drop in blood pressure. Check with your prescriber before starting.

Interactions & Conflicts

Interactions and cautions

Interacts with	Severity	Mechanism	Action
Nitrate medication	high	Additive nitric oxide mediated vasodilation	Avoid the combination
PDE5 inhibitors such as sildenafil	high	Amplified cyclic GMP signalling	Do not combine without medical advice
Antihypertensive drugs	moderate	Additive blood pressure lowering	Monitor for dizziness and low readings when starting
Chronic kidney disease	moderate	Conversion to arginine occurs in the kidney	Seek medical advice before use
Pregnancy and breastfeeding	moderate	Safety data at supplemental doses are limited	Avoid unless advised otherwise
Upcoming surgery	low	Vasodilatory effect may interact with anaesthesia	Mention it during pre-operative assessment

References

Frequently Asked Questions

Medical Disclaimer

The information provided on this website is for educational and informational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or before starting any supplement regimen.

Individual results may vary. The statements on this website have not been evaluated by the Food and Drug Administration. Products and information are not intended to diagnose, treat, cure, or prevent any disease.