It seems likely that tablets taken as emergency contraception are not good for everyday usage. Emergency contraception pills can cause irregular vaginal bleeding. You can consider taking a day-to-day contraceptive birth control pill. One of the side effects of contraceptive pills could be weight gain. Gaining weight can be due to 2 reasons: the anabolic effect of the progesterone component in the pills, and an increase in appetite. Increase in appetite is considered the more important reason for weight gaining. You might consider using low-dose contraceptive pills and following a proper diet you can prevent this side effect.