Norethisterone is a synthetic form of the naturally occurring hormone in your body called progesterone.
Therefore, it mimics the action of progesterone and can delay your period when taken 3 days before your period is due to start. The body sheds your womb lining, which is what your period consists of; when the progesterone levels in your normal monthly cycle begin to fall. By increasing the progesterone levels we can delay this process.
Even though norethisterone mimics progesterone, a hormone also in contraceptive pills, it cannot be used as birth control. It also cannot be used in conjunction with the combined contraceptive pill but can be used with the mini (progesterone only) pill. Norethisterone should not be taken by pregnant or breastfeeding women.