Mechanism of action of the “morning after pill
The principle of action of the emergency contraceptive pill consists mainly in the prompt inhibition or delay of ovulation. Depending on the active ingredient, ovulation can be delayed by 5 days (ulipristal acetate) or 3 days (levonorgestrel). The active ingredients, ulipristal acetate and levonorgestrel, suppress the hormone LH (luteinizing hormone), which is necessary for ovulation, by blocking the LH receptor.
As a result, the LH peak, which is important for ovulation, does not occur. This prevents ovulation with the formation of an egg capable of fertilization and an unwanted pregnancy. However, if ovulation has already occurred at the time of taking the pill, the effect of the “morning after pill” is powerless, as it does not prevent fertilisation itself or the implantation of the egg in the uterus, but only postpones the time of ovulation. For this reason it is important to take the emergency contraceptive pill as soon as possible after unprotected sexual intercourse.
When is the “morning after pill” taken?
If ovulation has already occurred during or shortly after unprotected sexual intercourse, pregnancy can no longer be prevented by the effectiveness of the emergency contraceptive pill. For this reason, gynaecologists and pharmacists ask about regularity, average cycle length and the exact day on which sexual intercourse took place. This allows the approximate time of ovulation to be calculated and the effect of the emergency contraceptive pill to be estimated.
If unprotected sexual intercourse took place 1-2 days before ovulation, it is recommended to take the “morning after pill”. However, if unprotected sex took place on the day of ovulation or a few days later, the effect of the emergency contraceptive pill is no longer guaranteed. In these cases, implantation of the “contraceptive coil” may be recommended or abortion methods may be used. If sexual intercourse takes place in the second half of the cycle (i.e. shortly before menstruation), it is usually no longer necessary to take the morning-after pill, as the egg is no longer capable of fertilization at this point.
