This is a general recommendation applicable to all neuropathic pain syndromes except for trigeminal neuralgia.In regard to the specific diagnoses, the best evidence exists for gabapentin treatment of postherpetic neuralgia and diabetic neuropathy. Gabapentin is approved for the former indication in the US. In addition to these two neuropathies, European Federation of Neurological Societies guideline notes gabapentin effectiveness for central pain. A combination of gabapentin with an opioid or nortriptyline may work better than either drug alone.Overall, gabapentin shows moderate effectiveness for neuropathic pain. Only a minority of patients obtain meaningful relief. Out of 10 persons treated with gabapentin, three to four benefit substantially as compared to one to two persons treated with placebo.Evidence finds little or no benefit and significant risk in those with chronic low back pain or sciatica. Gabapentin is not effective in HIV-associated sensory neuropathy and neuropathic pain due to cancer. Anxiety
There is a small amount research on the use of gabapentin for the treatment of anxiety disorders. In a controlled trial of breast cancer survivors with anxiety, and in a trial for social phobia, gabapentin significantly reduced anxiety levels. For panic disorder, gabapentin is ineffective. Conversely, some psychiatric textbooks see "a possible role for gabapentin in anxiety disorders, particularly social phobia and panic disorder" based on "case reports and double-blind studies" or state that controlled studies have not shown gabapentin to be very effective for psychiatric indications; "however, clinically it is effective". Sleep
Gabapentin is effective in treating sleep disorders such as insomnia and restless legs syndrome.
Subsequent to 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 (see below). Reuters reported on 25 March 2010, that "Pfizer Inc violated federal racketeering law by improperly promoting the epilepsy drug Neurontin ... Under federal RICO law the penalty is automatically tripled, so the finding will cost Pfizer $141 million." The case stems from a claim from Kaiser Foundation Health Plan Inc. that "it was misled into believing Neurontin was effective for off-label treatment of migraines, bipolar disorder and other conditions. Pfizer argued that Kaiser physicians still recommend the drug for those uses", and that "the insurers website also still lists Neurontin as a drug for neuropathic pain. "The Wall Street Journal noted that Pfizer spokesman Christopher Loder said, "We are disappointed with the verdict and will pursue post-trial motions and an appeal." He later added that "the verdict and the judges rulings are not consistent with the facts and the law." Franklin v. Parke-Davis case
While off-label prescriptions are common for a number of drugs, marketing of off-label uses of a drug is not. 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.