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: Gynaecology & Obstetrics
OCP's cause all except: 
Select and explain. 
A. Dysmenorrhea, B. Mastalgia, C. Nausea, D. Chloasma
A: Dysmenorrhea
Answer: A: Dysmenorrhea 
Explanation: None