How does period delay medication work and when should I take it?

Period delay medication, such as Norethisterone, works by artificially keeping your natural progesterone levels high, which prevents the lining of your womb from shedding and delays the onset of your period. To be effective, you must start taking the tablets exactly three days before your period is due to begin. You continue taking the tablets for as long as you wish to delay your cycle (up to a maximum of 17 days). Your period will normally start two to three days after you stop taking the medication. Please note that period delay tablets are not a form of contraception and will not prevent pregnancy.