The purpose of this study is to determine the efficacy and tolerability of 500 mg and 1000 mg Aspirin® (study medication) by comparing it to placebo (the control group without active substance) or 200 mg or 400 mg Ibuprofen (study medication) in treating the symptoms of episodic tension-type headache. The study is designed to develop a treatment method against episodic tension-type headache which will have more advantages for patients than the methods that are currently available.