LisaBa, That is correct, If you study a 1,000 couples using the pill for 12 months as directed, between 3 and 10 couples will be pregnant at the end of the year (the variation from 3 to 10 is due to the different types of pills, triphasic, monophasic, mini, combination etc..). That is between 3 and 10 failures out of 13,000 cycles. That is pretty good odds and pretty close to 100% effective.
It is thought that most of the failures happens when the women take medicines that negate the pill's actions but there are also some genuine failures.
Your best bet of being 100% safe is to use condoms as well as the pill. That way you also protect yourself from infections and STDs and you also do not have to freak out when the condom fails as you have pretty good protection against pregnancy from the pill.
Condoms are not 100% effective either but it's true that when combined with birth control they drasticly increase your safety. There are really no guarentees in life. Follow birth control instructions carefully, don't take foolish chances with your health or future out of sexual urgency, and more than likely you're not going to have any problems.
Only thing that is 100% effective is not having sex at all.
Nothing from pill to shot or a condom is 100% effective. You always have a chance of getting pregnant. That is why some couples use pills and also a condom just for bigger security. But chances of getting pregnant while on pills are very low.
"Only thing that is 100% effective is not having sex at all. "
Thanks to the USA's experiment with abstinence only education from 2001 to 2008, we know that it is not true. Abstinence has a pretty high failure rate.
The past decade has shown that good intentions are not a good birth control method. Abstinence is 100% effective with perfect use but for normal use, it gets pretty close to withdrawal in normal use. Recent studies have shown that abstinence postpones first time sex by 3 months, an abstinence pledge postpone it by 12 months but the net result of it is a slightly higher pregnancy and abortion rate and a much higher STD infection rate.
In some European countries, the combination of hormonal birth control and condoms are taught to young people. (abstinence is taught as a lifestyle choice, not a birth control method.) They have an almost non-existent unwanted pregnancy rate in those countries (0.5 per 100 vs. 5.5 per 100 in the USA).
(Sorry ClearR, I know you did not mean it this way but it still is worth it to look at the facts around the 100% effective abstinence only claims.)