Side-by-side comparison of mechanisms, dosing, interactions, and stacking potential.
| Fasoracetam | Phenibut | |
|---|---|---|
| Category | Nootropics | Nootropics |
| Standard Dose | 20-100 mg 1-3 times daily (sublingual or oral) | 250-750 mg as needed, maximum 1-2 times per week (for educational context — carries significant dependence risk) |
| Timing | Morning and afternoon. Sublingual administration may provide faster onset and higher bioavailability. With or without food. | On an empty stomach (food significantly reduces absorption). Onset 2-4 hours. Effects last 4-8 hours with residual effects up to 24 hours. Half-life approximately 5.3 hours. |
| Cycle Duration | Cycles of 4-8 weeks on, 2-4 weeks off. Limited long-term safety data. | STRICTLY intermittent use only — maximum 1-2 times per week. NEVER use daily for more than 1 week. Tolerance develops within days, leading to dose escalation and dependence. |
| Evidence Level | animal_plus_anecdotal | moderate_human |
Non-classical racetam that modulates all three groups of metabotropic glutamate receptors (mGluR Groups I, II, and III) and upregulates GABA-B receptors — a unique mechanism that distinguishes it from other racetams. Also enhances high-affinity choline uptake (HACU) and stimulates acetylcholine release. Does not significantly affect adrenergic, serotonergic, or dopaminergic receptors. The GABA-B upregulation is particularly notable as it may counteract GABA-B receptor downregulation caused by phenibut or baclofen tolerance.
20-100 mg 1-3 times daily (sublingual or oral)
Morning and afternoon. Sublingual administration may provide faster onset and higher bioavailability. With or without food.
Cycles of 4-8 weeks on, 2-4 weeks off. Limited long-term safety data.
Beta-phenyl derivative of GABA that crosses the blood-brain barrier (unlike GABA itself) due to the addition of a phenyl ring. Acts as a full agonist at GABA-B receptors with 30-68x lower affinity than baclofen, requiring correspondingly higher doses. Also binds to and blocks alpha-2-delta subunit-containing voltage-dependent calcium channels (VDCCs), making it a gabapentinoid similar to gabapentin and pregabalin. At low concentrations, mildly increases dopamine levels in the brain, providing stimulatory and nootropic effects alongside anxiolysis. Weak agonist activity at GABA-A receptors at higher doses.
250-750 mg as needed, maximum 1-2 times per week (for educational context — carries significant dependence risk)
On an empty stomach (food significantly reduces absorption). Onset 2-4 hours. Effects last 4-8 hours with residual effects up to 24 hours. Half-life approximately 5.3 hours.
STRICTLY intermittent use only — maximum 1-2 times per week. NEVER use daily for more than 1 week. Tolerance develops within days, leading to dose escalation and dependence.
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