The most common reason contraceptive pills lose efficacy is because they are not taken on time everyday. If you struggle to remember to take your pill on time, set a recurring reminder on your mobile phone.
Apart from missed pills, there are other situations when contraceptive pills can lose efficacy:
If you have vomiting or diarrhoea, the pill may not be absorbed properly and it may stop working. You should use other contraceptives, such as a condom, during these times.
Some medications, such medicines that treat TB and HIV, and medicines against seizures, could also stop the pill from working. Always tell you doctor that you are on the pill before they give you other medications.
If you use the morning after pill, particularly ellaOne, the efficacy of the regular pill will be reduced for the next several days. Read more here.