The study starts with a 2-4 week run in phase. AM will be given as open-labelled 5 mg or 10 mg tablets, administered once daily. After randomization during the double-blind phase, study medication will comprise either OM/AM 40/10 mg or PER 8 mg (2x4 mg) plus AM 10 mg and will be administered once daily. Furthermore, open-label HCTZ 12.5 mg and 25.0 mg will be provided in tablets and administered once daily according to the treatment schedule.