#080 · Drug of the Day Gabapentinoid · α₂δ-1 Neurontin · neuropathic pain Controlled in many jurisdictions 2026-09-08

Gabapentin

Named after GABA. Does not bind GABA receptors.

1-(aminomethyl)cyclohexaneacetic acid · C9H17NO2 · MW 171.24 g/mol · CAS 60142-96-3 · Neurontin · ChEMBL CHEMBL940

Gabapentin (Neurontin). A gabapentinoid: it binds the α2δ-1 auxiliary subunit of voltage-gated calcium channels and reduces excitatory transmitter release. It is not a GABAA or GABAB agonist despite the name. Versus pregabalin #040: lower potency, saturable absorption (bioavailability falls as you climb the dose), and the same opioid-combination respiratory story that moved it onto controlled-substance lists in the UK and several US states.

Primary targetCaV α₂δ-1
Mechanism↓ channel trafficking / release
GABAA/BNo binding
AbsorptionSaturable (LAT1)
ClearanceRenal, unchanged
vs pregabalinWeaker · saturable
Opioids↑ overdose risk
01 · Mechanism of Action

The Name Is a Lie; the α2δ Pocket Is Not

Gabapentin binds a VWA-domain amino-acid pocket on α2δ-1 (the R217 locus on the pregabalin page). Occupancy reduces trafficking of CaV2.x to the membrane and cuts glutamate/substance-P release. Zero activity at GABA receptors. PDB 7VFS resolves human CaV2.2 with α2δ-1 in the apo state — same honest caveat as pregabalin #040: the drug is not in the map.

Absorption via system-L (LAT1) is saturable, so 300 mg is much more bioavailable than 1200 mg on a percent basis. That is why people 'dose three times a day' and why megadosing for euphoria hits a wall that pregabalin (more linear, more potent) does not. Renal clearance unchanged — dose by GFR.

① α2δ-1 VWA pocket

Amino-acid drug site, not a GABA site. R217 and the cache domain are the structural story.

② ↓ CaV trafficking

Fewer channels at the terminal → less excitatory release. Slow; not an immediate channel plug.

③ Zero GABA activity

Does not bind GABAA or GABAB. The name is 1970s marketing/chemistry, not mechanism.

④ Saturable LAT1

Bioavailability ~60% at 300 mg, ~30% at 1600 mg. Pregabalin is the more linear cousin.

⑤ Renal clearance

Unmetabolized. Adjust in CKD or you will stack sedation, ataxia, and myoclonus.

⑥ Misuse + opioids

Euphoria at high dose in some people; combination with opioids is over-represented in overdose deaths.

Gabapentin → α₂δ-1 occupancy → ↓ CaV at terminals → less glutamate release · analgesia / sedation
+ opioid → additive respiratory depression → this is the death combination
02 · Pharmacokinetics

Saturable In, Unchanged Out

Tmax ~2–3 h; t½ ~5–7 h. No CYP. Hemodialysis removes a chunk — supplement after dialysis. Antacids (Al/Mg) cut absorption.

Oral F (300 mg)~60%
Oral F (1600 mg)~30% (saturable)
Tmax~2 – 3 h
T½~5 – 7 h
MetabolismNone
ClearanceRenal unchanged
TransporterLAT1 / system L
vs pregabalinless potent, less linear
03 · Why This Became a Controlled Drug in Places

Not Heroin. Not Harmless in a Fentanyl Supply.

Gabapentinoids potentiate opioid respiratory depression. That epidemiology, plus prison/misuse markets, is why the UK scheduled gabapentin and why US states followed. Withdrawal is real (anxiety, insomnia, sweating, seizures rarely). Taper. See pregabalin #040 for the more potent, more linear sibling.

04 · FlexAIDΔS · Shannon Entropy Analysis

An Amino Acid Wedge, Not a Channel Plug

FlexAIDΔS · Entropy Commentary

Gabapentin is a constrained GABA analog that never found GABA receptors and instead occupied an amino-acid pocket on α2δ. Small ligand, low ΔS_conf, binding dominated by the carboxylate/amine zwitterion in a solvated VWA site. 7VFS shows the subunit, not the pose — same honesty as #040. The Shannon story is trafficking (fewer channels, fewer release sites) more than a single-frame dock.

05 · Harm Reduction

Opioids, Kidneys, and a Real Withdrawal

Named after GABA, behaves like a gabapentinoid, kills in combination like a depressant.

Opioid combination

  • Respiratory depression is additive — the overdose literature is not theoretical
  • Assume illicit opioids may already be in the mix

Renal dosing

  • Unchanged drug + low GFR = ataxia, sedation, myoclonus
  • Supplement after hemodialysis

Dependence / withdrawal

  • Taper; abrupt stop can seize (rarely) and will feel awful
  • Antacids reduce absorption — timing matters

Practice

FATAL COMBINATIONS: Gabapentin + opioids / benzos / alcohol → respiratory depression. Renal failure + usual doses → profound sedation. This is not a GABA-A drug and flumazenil will not reverse it.
3D · CaV2.2–α2δ-1 (apo, drug pocket empty) PDB: 7VFS
Loading structure from RCSB…
Receptor (refined cartoon)
Contact residues
Ligand (ball-and-stick)
Structure: 7VFS — human CaV2.2 + α2δ-1, apo (Gao, Yao & Yan, Nature 2021). No gabapentin is in the map — same honest label as pregabalin #040. The α2δ-1 VWA amino-acid pocket is the drug site. Rotate · scroll to zoom · right-drag to translate.
View on RCSB →

Receptor Binding Affinities

gabapentinoid
Target Affinity Rel. Action
α₂δ-1
CaV auxiliary subunit
Ki ~50–140 nM
[³H]gabapentin displacement
Ligand
α₂δ-2
related subunit
weaker
less CNS-relevant
Ligand
GABAA
benzo / orthosteric
none
name is misleading
No binding
GABAB
baclofen site
none
not phenibut/GHB
No binding
[³H]gabapentin displacement at α2δ (ChEMBL CHEMBL940). GABA receptor inactivity is the point. PDB 7VFS is apo CaV2.2–α2δ-1, as on pregabalin #040.