NAC (N-Acetyl Cysteine) vs NR (Nicotinamide Riboside)

Mechanism

NAC is a precursor to L-cysteine, the rate-limiting substrate for glutathione (GSH) synthesis via glutamate-cysteine ligase. It directly replenishes intracellular GSH, the master endogenous antioxidant. NAC also modulates glutamatergic neurotransmission by stimulating the cystine-glutamate antiporter (system Xc-), influencing extrasynaptic glutamate levels. Additionally, it acts as a mucolytic by cleaving disulfide bonds in mucus glycoproteins.

Standard Dosing

600-1200mg daily

Timing

On empty stomach for best absorption, 30 min before meals. Split doses if >600mg.

Cycle Duration

Cycle 8 weeks on, 2 weeks off (to avoid potential downregulation of endogenous GSH production)

Side Effects

• Nausea
• GI upset
• Sulfurous odor/taste
• Rare: skin rash
• Potential zinc/copper chelation at very high doses

Contraindications

• Active gastric ulcers (may increase gastric acid)
• Asthma (rare bronchospasm with inhaled form)
• Concurrent chemotherapy (discuss with oncologist)

Best Stacking Partners

Mechanism

NR is converted to NMN by nicotinamide riboside kinases (NRK1/NRK2), then to NAD+ via the salvage pathway. Like NMN, elevated NAD+ activates sirtuins, PARPs, and CD38. NR has demonstrated ability to cross the blood-brain barrier and elevate brain NAD+ levels. It supports mitochondrial function, DNA repair, and circadian rhythm regulation through SIRT1-mediated deacetylation of BMAL1 and CLOCK proteins.

Standard Dosing

300-600mg daily

Timing

Morning with or without food.

Cycle Duration

ongoing

Side Effects

• Mild nausea
• Warmth/flushing (mild)
• GI upset
• Fatigue in some during initial days

Contraindications

• Active cancer (same theoretical NAD+ concern as NMN)
• Pregnancy/lactation
• Theoretical cancer concern shared with NMN

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