Nootropic

S-Phenylacetyl L-Glutathione

Also known as: S-Phenylacetyl Glutathione, SPAG, Phenylacetyl Glutathione, N-Phenylacetyl-L-Glutathione

Evidence

S-Phenylacetyl L-Glutathione is a modified form of glutathione designed for improved bioavailability and potential blood-brain barrier penetration. Limited human evidence exists; most data is from cell culture and animal studies.

Last reviewed June 2026 · Evidence graded from peer-reviewed research, not editorial opinion. Educational only — not medical advice.

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Primary uses

Cognitive support
Antioxidant defense
Neuroprotection

How it works

Delivers glutathione or its precursors across the blood-brain barrier
May enhance intracellular glutathione levels
Potential antioxidant and free radical scavenging activity

Dosage

Typical range: 200-400 mg daily
Timing: No established optimal timing; morning dosing suggested
With food: May be taken with or without food
Duration: Long-term safety and efficacy duration unclear due to limited research
Special populations: Insufficient data for pregnant/nursing women, children, or those with severe liver disease

Forms

Capsule· 70/100
Powder· 70/100

Safety

Common side effects

Generally well-tolerated; specific adverse event data limited

Contraindications

Caution in individuals with severe liver or kidney impairment
Insufficient safety data in pregnancy and lactation

Evidence notes

Very limited human clinical data. Mechanism is theoretically sound but empirical evidence in humans is sparse. Most supporting evidence comes from in vitro studies and animal models. No large RCTs in human populations.

Grade D: Primarily pre-clinical or anecdotal; human efficacy not established.

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Medical disclaimer. This page is educational and does not replace advice from a qualified healthcare provider. Individual needs and risks vary — consult a professional before starting, stopping, or combining supplements, especially if you are pregnant or nursing, taking medication, or managing a health condition.