Not really true. This is from Planned Parenthood:
Starting Birth Control Pills
Women used to be told that they could only start the pill on the first day of their period or on the first Sunday after the start of their period. We now know that it’s also perfectly fine to start the pill on any day of the month. Talk with your health care provider about what day is best for you to start taking the pill.
Combination Pills
Combination pills have two hormones — estrogen and progestin.
You may start the combination pill at any time:
If you start within five days after the start of your period, you are protected against pregnancy right away. You will not need to use a backup method of birth control. That means that if your period starts on a Wednesday morning, you can start the pill up to Monday morning to be protected right away.
If you start at any other time during your menstrual cycle, you will be protected from pregnancy after seven days. Use another method of birth control — like a condom, female condom, diaphragm, or sponge — if you have vaginal intercourse during the first week of use.
Progestin-Only Pills
You may start the progestin-only pill at any time. Use another method of birth control if you have vaginal intercourse during the first 48 hours of progestin-pill use — protection will begin after two days.
Taking the progestin-only pill at the same time each day is essential. If you take it more than three hours past the regular time, you need to use a backup method of birth control for 48 hours after taking the late pill.
Please use back up for the first month or two- there is not a 100% guarantee that it will be effective for at least a month or two. Also, it is easier to do the Sunday start day... you start taking your first pill on the Sunday after you have started your period- even if you are still on your period.
If you ever miss a pill be sure to follow the directions and take the missed pill(s) on schedule and use back up! Remember when you start having sex you need to understand that you can get pregnant even when you follow all of the necessary precautions.
you will never acheive immediate effect the first day you take it.
from my understanding of the birth control i use to take, you take the first pill on the sunday after you get off your period
your never safe. birth controls never 100%. it DOES NOT work right away and takes a month or two to actually start protecting you.