Gabapentin (Neurontin) acts to inhibit calcium channels in the brain neurons, thus reducing activity. It is approved for use as adjunct therapy in partial and secondarily generalized seizures, to be added when older drugs are not giving satisfactory control. It is also FDA approved for reducing postherpetic pain(shingles). It has a larger therapeutic index than most other anti-seizure medications (phenytóin 3, Tegretol 8, valproate 1.7), and the least number of adverse effects. Extensive (and illegal) promotion has resulted in 80% of prescriptions being for unlabelled uses such as mood swings in bipolar disorder, neuralgic pain (diabetic neuralgic pain, shingles), nystagmus, Parkinson’s disease, and schizophrenia. Pfizer paid a $450 million dollar settlement for illegal advertising of off-label used of Neurontin. Adverse effects are relatively mild, as anti-seizure medications go. They include sedation and ataxia.