DOSEGUY

FGL

guinea pig

Also seen as: FGL peptide, NCAM mimetic peptide, FG loop peptide

The Dose Guy’s verdict
Sep 1, 2026
3 sources

FGL has strong animal data for memory and neuroprotection, and it cleared a phase 1 in healthy men with no alarms. That’s more clinical footing than most neuropeptides on this shelf. But two findings in healthy animals stop me from recommending it: FGL lowered the seizure threshold in mice, and it reduced hippocampal neuron counts in healthy young rats. Those aren’t toxicity at extreme doses. The seizure effect appeared at both dose levels the study tested. Until someone explains that tradeoff in humans, I’d watch this one, not run it.

Would I take it?Not yet. The safety signals in healthy animals need answers.

What it is

A synthetic 15-amino-acid peptide modeled on the part of NCAM, neural cell adhesion molecule, that binds fibroblast growth factor receptor 1. When FGL activates FGFR1, it triggers signaling cascades that promote neurite outgrowth, neuronal survival, and synaptic plasticity. In rats, that machinery translated into lasting memory improvements after a single dose and protection against amyloid-induced damage. FGL has been delivered intranasally and subcutaneously in animal work, and the phase 1 used intranasal dosing in 24 healthy men. On the nootropic shelf it sits near dihexa, except FGL has cleaner sourcing: no retractions, no integrity concerns, just a real safety question the animal work raised and nobody has answered yet.

What the research shows

A phase 1 for safety and PK, strong animal memory data, and two concerning safety findings that frame the whole picture:

Single intranasal doses of 25, 100, and 200 mg in 24 healthy men produced no clinically notable ECG, vital sign, or laboratory abnormalities. Three participants reported five adverse events, including nasal burning at the 200 mg dose and runny eyes at 25 mg.Clin Pharmacokinet 2007 · phase 1 · n=24
In a mouse kindling model, both 2 and 10 mg per kg FGL reduced the number of stimulations needed to induce a generalized seizure.ACS Chem Neurosci 2014 · mice
In healthy 4-month-old rats, subcutaneous FGL reduced dorsal hippocampal volume and total pyramidal neuron numbers in CA1 and CA3.Neurochem Res 2013 · young rats
No controlled human efficacy trial of FGL exists. The phase 1 measured safety and pharmacokinetics only.as of Aug 2026

Realistic protocols

I’m not writing a clean protocol for a compound that reduced hippocampal neurons in healthy young animals. The community runs FGL intranasally or subcutaneously, typically at doses extrapolated from the animal literature, in short cycles of a few weeks. If you run it, treat it as the experiment it is: go low, keep the cycle short, and be honest that nobody knows whether the neuron-loss finding translates to humans. The phase 1 dosed up to 200 mg intranasally in a single sitting with no acute problems, but a single dose and a repeated course are different questions. For reference, a single 25 mg intranasal dose did not produce detectable plasma levels, and mean peak plasma at 100 mg was 0.52 ng per mL. If the memory-peptide angle interests you, dihexa has more community mileage.

Side effects

The phase 1 was uneventful. The animal signals are the concern:

monitorNasal burning at the 200 mg intranasal dose, reported by 2 of 24 participants. Resolved in under three minutes.
unknownIn healthy young rats, FGL reduced hippocampal volume and neuron counts. In mice, it lowered seizure threshold. If you have a seizure history or take anything that lowers seizure threshold, this is a hard no. These findings have not been studied in humans.
unknownNo repeated-dose human safety data exists. The phase 1 was a single dose.

Where to buy

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