Thanks for the query to ATD for an opinion.
Firstly there are no pills which are monthly oral contraceptive pills which get effective in preventing pregnancy from the first pill itself. It's not like that. It is dependent totally as to when the pill has been started, at which phase of the menstrual cycle.
If it has been started in the mid-cycle, close to the ovulation time then it would require 2 weeks to build up the hormone levels and then can be effective after that. But then one has to practice barrier contraception for the remaining month as ovulation is not prevented and pregnancy can still occur, in that case.
The correct time to start an OC pill is from day 2 of a fresh cycle , when ovulation period is away by 2 weeks and the pill has enough time to build up its levels and hence prevent ovulation by the mid-cycle and be effective throughout the cycle. Also initial 10 days are the safe period and any sex in that period is not liable to end in pregnancy as well, so if you have started the pack from day 2 of the cycle and have had 3 unprotected intercourse till now in these 5 days, then you are protected naturally, being in safe period, rather than the birth control pill at present.
The effect of birth control in the first cycle can be seen after 2 weeks, when it inhibits ovulation and promotes contraception.
I hope I have answered your query in detail,
Wishing you good health,
These Q&A’s are for educational purposes and should not be relied upon as a substitute for medical advice you may receive from your physician. If you have a medical emergency, please call 911. These answers do not constitute or initiate a patient/doctor relationship.