Contraceptive pills. Oral contraceptive pills used for birth control. Dates are present on the 21 pill pack to ensure that the correct daily dose is taken. The contraceptive pill contains one or more synthetic female sex hormones Most contraceptive pills consist of both progesterone & oestrogen. Progesterone acts on the pituitary gland affecting the menstrual cycle; oestrogen blocks the monthly release of a mature egg (ovula- tion). The unwanted pregnancy rate is less than 1 per 100 woman years. Side effects from using the pill include headache, weight gain, nausea & higher risks of cervical cancer & thrombosis.