Core study: Week 0 to Week 18 Once daily placebo.

Extension study:

Week 19 to Week 22 Once daily placebo, Week 23 Once daily perampanel 2 mg/day, Week 24 Once daily perampanel 4 mg/day, Week 25 Once daily perampanel 6 mg/day, Week 26 Once daily perampanel 8 mg/day, Week 27 Once daily perampanel 10 mg/day, Week 28 to Week 75 or more Once daily perampanel 12 mg/day.

Seizure frequency was based on number of seizures per 28 days, calculated as the number of seizures over the entire time interval divided by the number of days in the interval and multiplied by 28. A complex partial seizure is a type of seizure that arises in one lobe of the brain, rather than the whole brain and it affects awareness and may cause in loss of consciousness. Secondary generalized seizures begin in one part of the brain, but then spread to both sides of the brain.

The investigator evaluated each participant for CGIC questionnaire to assess change in participant's disease clinical status from baseline. Assessment evaluated frequency of seizures, severity of seizures, occurrence of adverse events (AEs), and overall functional status of the participant using the 7-point scale. The evaluation used a 7-point scale with the scores 1: Very much improved, 2: Much improved, 3: Minimally improved, 4: No change, 5: Minimally worse, 6: Much worse, 7: Very much worse. Lower score indicated improvement and higher score indicated worsening.

Participants received perampanel 2 mg tablet, orally, once daily before bedtime in Week 0 and then titrated up to maximum dose of 4 mg orally, once daily from Week 1 up to Week 5 (titration period), followed by perampanel 4 mg, orally, once daily from Week 6 up to Week 18 (maintenance period) in the Core Phase. Total duration of titration and maintenance period in Core Phase was 19 weeks. Participants received the same dose of perampanel 4 mg in Extension Phase as they received in Core Phase, orally, once daily before bedtime from Week 19 to Week 22 (preconversion period). Participants started receiving perampanel 4 mg tablet, orally, once daily which was then titrated as 2 mg weekly increments up to a maximum dose of 12 mg, orally, once daily up to Week 28 (conversion period). All participants could have their dose down or up titrated until an optimal dose was reached. After the conversion period, participants entered a maintenance period in which they received the perampanel dose orally, once daily, that provided the optimal combination of efficacy and tolerability before bedtime up to Week 75 or longer depending on the requirements of each country in the Extension Phase.

Participants received perampanel 2 mg tablet, orally, once daily before bedtime in Week 0 and then titrated up to maximum dose of 8 mg (weekly increment of 2 mg from Week 1 up to Week 3) orally, once daily for up to Week 5 (titration period), followed by perampanel 8 mg, orally, once daily from Week 6 up to Week 18 (maintenance period) in the Core Phase. Total duration of titration and maintenance period was 19 weeks in the Core Phase. Participants received the same dose of perampanel 8 mg in the Extension Phase as they received in Core Phase, orally, once daily before bedtime from Week 19 to Week 22 (preconversion period). Participants started receiving perampanel 8 mg tablet, orally, once daily which was then titrated as 2 mg weekly increments up to a maximum dose of 12 mg, orally, once daily up to Week 28 (conversion period). All participants could have their dose down or up titrated until an optimal dose was reached. After the conversion period, participants entered a maintenance period in which they received the perampanel dose orally, once daily, that provided the optimal combination of efficacy and tolerability before bedtime up to Week 75 or longer depending on the requirements of each country in the Extension Phase.

Participants received perampanel 2 mg tablet, orally, once daily before bedtime in Week 0 and then titrated up to maximum dose of 12 mg (weekly increment of 2 mg from Week 1 up to Week 5) orally, once daily for up to Week 5 (titration period), followed by perampanel 12 mg, orally, once daily from Week 6 up to Week 18 (maintenance period) in the Core Phase. Total duration of titration and maintenance period was 19 weeks in the Core Phase. Participants received the same dose of perampanel 12 mg in the Extension Phase as they received in Core Phase, orally, once daily before bedtime from Week 19 to Week 22 (preconversion period) and continued receiving perampanel 12 mg, orally, once daily up to Week 28 (conversion period). All participants could have their dose down or up titrated until an optimal dose was reached. After the conversion period, participants entered a maintenance period in which they received the perampanel dose orally, once daily, that provided the optimal combination of efficacy and tolerability before bedtime up to Week 75 or longer depending on the requirements of each country in the Extension Phase.