Gabapentin, sold under the brand name Neurontin among others, is an anticonvulsant medication primarily used to treat neuropathic pain and also for partial seizures[10][7] of epilepsy.

[12] Gabapentin, like other gabapentinoid drugs, acts by decreasing activity of the α2δ-1 protein, coded by the CACNA2D1 gene, first known as an auxiliary subunit of voltage gated calcium channels.

[18][19] During the 1990s, Parke-Davis, a subsidiary of Pfizer, used a number of illegal techniques to encourage physicians in the United States to prescribe gabapentin for unapproved uses.

[25] There is concern regarding gabapentin's off-label use due to the lack of strong scientific evidence for its efficacy in multiple conditions, its proven side effects and its potential for misuse and physical/psychological dependency.

[11][33] Regarding the specific diagnoses, a systematic review has found evidence for gabapentin to provide pain relief for some people with postherpetic neuralgia and diabetic neuropathy.

[39][38][27] Gabapentin is effective in treating sleep disorders such as insomnia and restless legs syndrome that are the result of an underlying illness, but comes with some risk of discontinuation and withdrawal symptoms after prolonged use at higher doses.

A clinical study in Iran, where heroin dependence is a significant social and public health problem, showed gabapentin produced positive results during an inpatient therapy program, particularly by reducing opioid-induced hyperalgesia and drug craving.

[68] Case studies indicate that it may cause anorgasmia and erectile dysfunction,[69] as well as myoclonus[70][71] that disappear after discontinuing gabapentin or replacing it with other medication.

[74] A large Swedish study suggests that gabapentinoids are associated with an increased risk of suicidal behaviour, unintentional overdoses, head/body injuries, and road traffic incidents and offences.

[75] On the other hand, a study published by the Harvard Data Science Review found that gabapentin was associated with a significantly reduced rate of suicide.

[76] Serious breathing suppression, potentially fatal, may occur when gabapentin is taken together with opioids, benzodiazepines, or other depressants, or by people with underlying lung problems such as COPD.

[78] Withdrawal symptoms typically occur 1–2 days after abruptly stopping gabapentin (almost unambiguously due to extended use and during a very short-term rebound phenomenon) — similar to, albeit less intense than most benzodiazepines.

[79] Agitation, confusion and disorientation are the most frequently reported, followed by gastrointestinal complaints and sweating, and more rare tremor, tachycardia, hypertension and insomnia.

[79] In some cases, users experience withdrawal seizures after chronic or semi-chronic use in the absence of periodic cycles or breaks during repeating and consecutive use.

[81] Through excessive ingestion, accidental or otherwise, persons may experience overdose symptoms including drowsiness, sedation, blurred vision, slurred speech, somnolence, uncontrollable jerking motions, and anxiety.

[88][89] Accordingly, while gabapentin has nanomolar affinity for the α2δ subunit, its potency in vivo is in the low micromolar range, and competition for binding by endogenous L-amino acids is likely to be responsible for this discrepancy.

[92] At very high concentrations gabapentin can suppress the growth of cancer cells, presumably by affecting mitochondrial catabolism, however, the precise mechanism remains elusive.

A process for chemical synthesis and isolation of gabapentin with high yield and purity[107] starts with conversion of 1,1-cyclohexanediacetic anhydride to 1,1-cyclohexanediacetic acid monoamide and is followed by a 'Hofmann' rearrangement in an aqueous solution of sodium hypobromite prepared in situ.

Gabapentin was designed, synthesized and tested in mice by researchers at the pharmaceutical company Goedecke AG in Freiburg, Germany (a subsidiary of Parke-Davis).

[108] Shortly after, gabapentin was shown in vitro to reduce the release of the neurotransmitter dopamine from slices of rat caudate nucleus (striatum).

Initial clinical trials utilizing small numbers of subjects were for treatment of spasticity[111] and migraine[112] but neither study had statistical power to allow conclusions.

[17] An extended-release formulation of gabapentin for once-daily administration, under the brand name Gralise, was approved in the United States for the treatment of postherpetic neuralgia in January 2011.

After the corporate acquisition of the original patent holder, the pharmaceutical company Pfizer admitted that there had been violations of FDA guidelines regarding the promotion of unproven off-label uses for gabapentin in the Franklin v. Parke-Davis case.

[20] In 2004, Warner-Lambert (which subsequently was acquired by Pfizer) agreed to plead guilty for activities of its Parke-Davis subsidiary, and to pay $430 million in fines to settle civil and criminal charges regarding the marketing of Neurontin for off-label purposes.

The 2004 settlement was one of the largest in U.S. history up to that point, and the first off-label promotion case brought successfully under the False Claims Act.

[142] Gabasync was marketed by Hythiam, Inc. which is owned by Terren Peizer, a former junk bond salesman who has since been convicted of securities fraud relative to another company.

[146] In November 2011, the results of a double-blind, placebo-controlled study (financed by Hythiam and carried out at UCLA) were published in the peer-reviewed journal Addiction.

The study, which analyzed healthcare data across 65 countries/ regions, found that the consumption rate of gabapentinoids had doubled over the decade, driven by their use in a wide range of indications.

When taken in excess, gabapentin can induce euphoria, a sense of calm, a cannabis-like high, improved sociability, and reduced alcohol or cocaine cravings.

[171] In cats, gabapentin can be used as an analgesic in multi-modal pain management,[172] anxiety medication to reduce stress during travel or vet visits,[173] and anticonvulsant.