This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Contraception, Subject name: Gynaecology & Obstetrics
A woman was taking progestin only pill for contraception. Which side-effect is not likely to occur : 
Select and explain. 
A. Acne, B. Amenorrhea, C. Dysmenorrhea, D. Obesity
C: Dysmenorrhea
Answer: C: Dysmenorrhea 
Explanation: Drawbacks of progesterone only pill Irregular bleeding Amenorrhea Weight gain Acne Migraine Headache Depression Ectopic pregnancy Breast cancer Thromboembolism Ref: Shaw Gynecology 17 e pg 266.