To compare outcomes over 12 months of treatment with antiepileptic drugs (AEDs) alone or vagus nerve stimulation (VNS) therapy plus AEDs in patients who have partial seizures refractory to at least two, but not more than five, AEDs.

Published data suggest that patients who continue to experience seizures after trials of two or three AEDs are unlikely to become seizure-free with further attempts at pharmacotherapy. Such patients may experience poor quality of life and functional outcomes from continuing seizures and the adverse effects associated with further attempts at pharmacotherapy. VNS is a non-pharmacologic treatment for epilepsy with well-established effectiveness as an adjunctive treatment (to AEDs) for partial seizures refractory to AEDs, but there are no randomized clinical trials comparing the effectiveness of adjunctive VNS therapy with further pharmacotherapy alone in such patients.

Inclusion Criteria:

• Patient has a diagnosis of partial seizures with onset before age 50, and the patient's prior electroencephalography and magnetic resonance imaging studies are consistent with the diagnosis of partial seizures.
• Patient has at least 4 complex partial seizures, but less than 25 seizures (any type), per month during the 3 months preceding randomization; for the 8 weeks preceding randomization, the seizure frequency should be confirmed from a patient diary.
• Patient has not had an adequate response to an adequate dosage of -- or was intolerant to -- a minimum of 2 different AEDs.
• Patient has (in the investigator's judgment) sufficient impairment from his/her epilepsy and/or epilepsy treatment that the potential benefits/risks of VNS therapy are warranted.
• Patient must currently be receiving at least one AED, but not more than three AEDs, in a stable dosage regimen for at least one month before randomization.
• Patient must be 12 years of age or older.
• Patient must be able to provide reliable seizure counts and to complete the evaluations specified in the study procedures flow chart.
• Patient must provide written informed consent, or legal guardian must give written permission and the minor provide written assent.

Exclusion Criteria:

• Patient has a history (lifetime) of having received more than 5 different AEDs.
• Patient has had a bilateral or left cervical vagotomy.
• Patient currently uses, or is expected to use during the study, short-wave diathermy, microwave diathermy, or therapeutic ultrasound diathermy.
• A VNS Therapy System implant would (in the investigator's judgment) pose an unacceptable surgical or medical risk for the patient.
• Patient is expected to require full body magnetic resonance imaging during the clinical study.
• Patient has had a previous VNS Therapy System implant.
• Patient has a previous neuroimaging study that demonstrates mesial temporal sclerosis, cortical dysplasia, or a suspected brain tumor.