4-Fluorophenibut (developmental code name CGP-11130; also known as ò-(4-fluorophenyl)-ó-aminobutyric acid or ò-(4-fluorophenyl)-GABA) is a GABA<sub>B</sub> receptor agonist which was never marketed. It is selective for the GABA<sub>B</sub> receptor over the GABA<sub>A</sub> receptor (IC<sub>50</sub> = 1.70 üM and > 100 üM, respectively). The drug is a GABA analogue and is closely related to baclofen (ò-(4-chlorophenyl)-GABA), tolibut (ò-(4-methylphenyl)-GABA), and phenibut (ò-phenyl-GABA). It is less potent as a GABA<sub>B</sub> receptor agonist than baclofen but more potent than phenibut.
The substance is sometimes referred to as 4F-phenibut, F-phenibut, or baflofen, and colloquially as fluorobut.
F-Phenibut is a prohibited substance in Lithuania and Hungary.