This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Analgesic that itself can cause headache as a side effect is : 
Select and explain. 
A. Indomethacin, B. Mefenamic acid, C. Piroxicam, D. Aspirin
A: Indomethacin
Answer: A: Indomethacin 
Explanation: None