L-Citrulline vs Taurine

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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Mechanism

Taurine is a sulfonic acid amino acid (not incorporated into proteins) with diverse physiological roles. It is the most abundant free amino acid in excitable tissues (heart, brain, retina, muscle). Mechanisms: GABA-A receptor agonism (inhibitory neurotransmission), glycine receptor agonism, osmoregulation (cell volume regulation via taurine transporter TauT), bile acid conjugation (taurocholate formation for fat digestion), calcium handling in cardiomyocytes (modulates RyR2/SERCA2a), mitochondrial protein synthesis (taurine modification of mitochondrial tRNA), and potent antioxidant (directly scavenges HOCl, stabilizes membranes). Recently identified as a longevity-associated molecule — taurine levels decline with age and supplementation extends lifespan in mice.

Standard Dosing

1000-3000mg daily

Timing

Flexible. Evening preferred for sleep/relaxation benefits. Pre-workout for cardiac and exercise performance benefits.

Cycle Duration

ongoing

Side Effects

• Generally extremely well-tolerated
• Mild GI discomfort
• Drowsiness at high doses
• Rare: hypothermia in preclinical data

Contraindications

• Bipolar disorder on lithium (monitor levels)
• Severe renal impairment
• Caution with severe renal impairment

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