Structural Comparison
A shared backbone, different substituents, structure only.
Several research compounds derive from the GABA scaffold. This comparison is strictly structural and chemical — it does not compare biological effects.
Structural comparison
- Phenibut4-amino-3-phenylbutanoic acid — GABA with a phenyl group at C-3
- Baclofen4-amino-3-(4-chlorophenyl)butanoic acid — GABA with a 4-chlorophenyl group at C-3 (a close structural relative of Phenibut)
- Pregabalin(S)-3-(aminomethyl)-5-methylhexanoic acid — a 3-substituted GABA analogue
- Gabapentin2-[1-(aminomethyl)cyclohexyl]acetic acid — GABA constrained on a cyclohexane ring
What the comparison shows
All four share a GABA-derived amino-acid backbone; they differ in the substituent and its position. Phenibut and baclofen are the most closely related, differing chemically by a single chlorine substituent on the aromatic ring. This page draws only structural parallels; for Phenibut’s own structure see molecular structure.
Formula and molar mass
The four differ measurably, not only on paper. Molar masses are quoted for the free bases in grams per mole; a salt form changes the figure, which is one reason a record should state the form it refers to (see free base versus hydrochloride).
- PhenibutC10H13NO2 — molar mass 179.22
- BaclofenC10H12ClNO2 — molar mass 213.66
- PregabalinC8H17NO2 — molar mass 159.23
- GabapentinC9H17NO2 — molar mass 171.24
Chirality separates them further
Phenibut and baclofen each carry one stereocentre, at the carbon bearing the aromatic ring, and are ordinarily encountered as racemates unless a record says otherwise. Pregabalin is defined as a single enantiomer — the S form is part of its identity, so a racemic sample is a different material rather than the same one at lower quality. Gabapentin has no stereocentre at all: its aminomethyl and acetic-acid arms hang from the same quaternary ring carbon, which is why it is drawn as a constrained analogue rather than a substituted one. Stereochemistry is therefore a second axis of difference on top of the substituent pattern, and it is discussed for this material on phenibut stereochemistry and enantiomers.
Telling them apart in the laboratory
Structural similarity is exactly what makes analytical confirmation worth doing. Phenibut and baclofen differ by a single chlorine, so they are close in retention on many reversed-phase methods but immediately distinguishable by mass spectrometry: chlorine occurs naturally as two stable isotopes in roughly a three-to-one ratio, so a chlorinated analogue shows a companion peak two mass units above the molecular ion at about a third of its height, and an unchlorinated one does not. Pregabalin and gabapentin are far enough apart in formula that exact mass alone separates them. Identity work of this kind is described under how laboratories verify chemical identity and, for this material specifically, analytical identification.
Regulatory standing is not shared
Structural kinship carries no regulatory consequence whatever. Baclofen, gabapentin and pregabalin are approved medicines in many jurisdictions and are supplied under the controls that attach to medicines there. Phenibut holds no such approval in the United States, is not a dietary ingredient, and is offered here strictly as a research material. The detail, with sources, is set out on legal and regulatory status.
What structural similarity does not establish
A shared backbone is a statement about atoms and bonds and nothing more. It licenses no inference about what any of these compounds does in a living system, and small structural changes are well known to produce entirely unrelated behaviour. This page is a chemist’s comparison of structures, formulas and analytical signatures; it is not a comparison of activity, and none is offered anywhere on this site.
For Research Use Only. Not for human or animal consumption. Nothing here is medical advice, a health claim, or usage guidance. No statement has been evaluated by the U.S. FDA. See our Disclaimer.