GABA (Gamma-Aminobutyric Acid) vs L-Citrulline

Mechanism

GABA is the primary inhibitory neurotransmitter in the CNS, activating GABA-A receptors (ligand-gated chloride ion channels, causing rapid inhibition) and GABA-B receptors (G-protein coupled, causing slow, sustained inhibition). Supplemental GABA's ability to cross the blood-brain barrier is debated — it likely acts primarily through the enteric nervous system (gut-brain axis), peripheral GABA receptors, and potentially via limited BBB penetration at the circumventricular organs. GABA promotes alpha brain waves (relaxation), increases growth hormone secretion (via GHRH modulation), and reduces sympathetic nervous system overactivation.

Standard Dosing

250-750mg daily

Timing

Evening before bed for sleep, or as needed for acute anxiety/stress. Sublingual onset: 15-20 minutes.

Cycle Duration

As needed or cycle 4-8 weeks on, 2 weeks off

Side Effects

• Drowsiness
• Tingling/flushing sensation (especially at higher doses — likely peripheral vasodilation)
• Mild shortness of breath sensation (transient)
• GI upset

Contraindications

• Severe respiratory depression
• Concurrent high-dose benzodiazepine use

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Mechanism

L-Citrulline is converted to L-arginine in the kidneys via argininosuccinate synthase and argininosuccinate lyase (bypassing hepatic first-pass metabolism that degrades oral L-arginine). L-arginine is then the substrate for endothelial nitric oxide synthase (eNOS), producing nitric oxide (NO). NO activates soluble guanylyl cyclase (sGC), increasing cGMP, causing vascular smooth muscle relaxation and vasodilation. Citrulline also participates in the urea cycle (ammonia detoxification), and supplementation increases plasma arginine more effectively than arginine supplementation itself due to bypass of intestinal and hepatic arginase.

Standard Dosing

3-6g L-citrulline daily or 6-8g citrulline malate

Timing

30-60 minutes pre-workout for exercise performance. For blood pressure: split AM/PM doses. Powder form in water.

Cycle Duration

ongoing

Side Effects

• Mild GI discomfort
• Bloating
• Headache (vasodilation)
• Generally very well-tolerated even at high doses

Contraindications

• Concurrent nitroglycerin/nitrate therapy
• Severe hypotension
• Urea cycle disorders (citrullinemia)

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