L-Citrulline is a watermelon-derived amino acid that raises arginine and nitric oxide, relaxing blood vessels. Its most reliable effect is lifting circulating arginine; signals for lower blood pressure, easier vessel widening, less muscle soreness, and modest strength gains are promising but uneven, clearest in older adults with higher blood pressure. Well tolerated; longevity claims stay early. (Full Review)

Protocol

Vascular Dose

3–6 g/day

Pure L-Citrulline, taken consistently

Performance Dose

6–8 g

Citrulline malate, ~60 min pre-training

Split Dosing

2 × 3 g/day

For blood-pressure goals, to sustain arginine

Time to effect

Blood Flow

~1 hour

Acute effect; plasma peaks ~1 h

Blood Pressure

4–8 weeks

Consistent daily use

Endothelial Function

4–8 weeks

Consistent daily use

Benefits

High: Increased nitric oxide and plasma arginine

Medium: Reduced blood pressure; reduced post-exercise muscle soreness and perceived exertion; enhanced high-intensity strength and power

Low: Improved erectile function; improved endothelial function and arterial stiffness; aerobic and endurance performance; favorable shifts in body composition

Speculative: Age-related muscle preservation; cardiovascular healthspan and longevity

Contraindications

Current nitrate use

Symptomatic low blood pressure (systolic below 90 mmHg)

Inherited urea-cycle disorders (except under specialist care)

Severe kidney impairment (eGFR below 30 mL/min/1.73 m²)

Scheduled surgery (stop 24–48 h before)

Key Interactions

Antihypertensives (ACE inhibitors, ARBs, calcium channel blockers)

PDE5 inhibitors (sildenafil, tadalafil)

L-Arginine and nitric-oxide supplements

Blood-pressure-lowering supplements (nitrate/beetroot, garlic, magnesium, potassium, coenzyme Q10)

Over-the-counter nitric-oxide pre-workout products

Risk & Side Effects

High: Mild gastrointestinal effects

Medium: Additive hypotension and dizziness

Low: Nitric-oxide-related headache or flushing

Speculative: Unknown long-term safety at high doses; theoretical promotion of viral replication via arginine

Monitoring

Marker	Target	Why
Blood Pressure	<120/80 mmHg	Primary target of vascular use
Resting Heart Rate	50–70 bpm	Context for cardiovascular status
Flow-Mediated Dilation	>7%	Direct readout of endothelial function
eGFR (kidney filtration)	>90 mL/min/1.73 m²	Kidney performs citrulline-to-arginine conversion
BUN	10–16 mg/dL	Reflects urea-cycle and kidney handling
Fasting Blood Glucose	70–85 mg/dL	Metabolic context; diabetes raises arginase
hs-CRP	<1 mg/L	General marker of inflammation affecting vessels

Cadence: Blood pressure at 1, 4, and 8 weeks, then every 6–12 months if used long term; kidney and metabolic markers every 6–12 months

Qualitative Assessment

Exercise tolerance and muscle fullness
Post-exercise soreness
Energy and lightheadedness
Erectile or circulatory quality

L-Citrulline for Health & Longevity

Protocol

Benefits

Risk & Side Effects

Monitoring

Qualitative Assessment