Final answer:
Emergency contraceptive pills, also known as morning-after pills, may cause nausea and vomiting as side effects. Weight gain or loss is also possible, although it is not common. It is important to note that emergency contraceptive pills do not affect fertility or blood pressure.
Step-by-step explanation:
Emergency contraceptive pills, also known as morning-after pills, are used as a backup method of birth control if the primary method fails. They should not be used as a regular form of birth control. These pills work by preventing ovulation, thinning the uterine lining, and altering the cervical mucus, which makes it difficult for sperm to reach the egg.
Some negative side effects of emergency contraceptive pills include nausea and vomiting, which can occur within a few hours of taking the pills. Another potential side effect is weight gain or loss, although it is not common. It is important to note that emergency contraceptive pills do not increase fertility and do not cause a decrease in blood pressure as mentioned in options C and D.