Arginine
L-Arginine
L-Arginine is a semi-essential amino acid that serves as the primary substrate for nitric oxide (NO) synthesis in the body. It is widely used to support cardiovascular health, improve exercise performance via enhanced blood flow, and promote growth hormone secretion. Clinically, it has been studied for erectile dysfunction, heart failure, and wound healing applications.
Mechanism of Action
L-Arginine is converted to nitric oxide and L-citrulline by the enzyme nitric oxide synthase (NOS), causing vasodilation through activation of soluble guanylate cyclase and subsequent cGMP-mediated smooth muscle relaxation. It also stimulates pituitary release of growth hormone and insulin, and serves as a precursor for creatine, polyamine, and proline biosynthesis. At higher doses, it activates mTOR signaling pathways relevant to muscle protein synthesis.
Evidence by Health Goal(18 goals)
Dosing Protocols
30-60 minutes before exercise or on an empty stomach for cardiovascular/performance effects; with meals to reduce gastrointestinal discomfort
Doses above 6g significantly increase risk of gastrointestinal side effects. Some evidence suggests L-Citrulline is more effective at raising plasma arginine levels due to better oral bioavailability and avoidance of hepatic first-pass metabolism. For growth hormone stimulation, single doses of 5-9g have been studied but GI tolerance is a limiting factor.
Safety & Side Effects
L-Arginine is generally well tolerated at doses up to 6g daily and has a strong safety record in healthy adults; however, high doses carry meaningful GI side effects and it should be avoided or used with caution in individuals with herpes simplex virus infections, low blood pressure, recent myocardial infarction, or those on nitrates and antihypertensives. It is not a prescription substance but post-MI supplementation has been associated with increased mortality in one clinical trial, warranting caution in cardiac populations.
Possible Side Effects
- !Gastrointestinal discomfort, bloating, and diarrhea at doses above 6-9g
- !Nausea, particularly when taken on an empty stomach at higher doses
- !Hypotension (low blood pressure) due to vasodilatory effects
- !Worsening of herpes simplex outbreaks by supporting viral replication
- !Electrolyte imbalances with very high chronic dosing
- !Headache associated with vasodilation
- !Potential worsening of asthma symptoms in susceptible individuals
Interactions
- -Potentiates effects of PDE5 inhibitors (sildenafil, tadalafil) - may cause excessive hypotension
- -Additive blood pressure lowering with antihypertensive medications - monitor closely
- -May enhance anticoagulant/antiplatelet effects of warfarin or aspirin via NO-mediated platelet inhibition
- -Antagonizes lysine availability - high-dose arginine may compete with lysine absorption, relevant in herpes management
- -May interact with blood glucose lowering medications by stimulating insulin secretion
Cost & Where to Buy
Bulk powder is the most cost-effective option at $0.05-0.10 per gram; capsule and tablet forms cost more per gram. Quality brands with third-party testing sit at the higher end of the range.
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