Cerazette, a progestin-only contraceptive pill, starts working immediately if it is taken within the first five days of a woman's menstrual cycle. However, if taken at any other time, it takes 48 hours to provide effective contraception. It primarily works by thickening the mucus in the cervix, making it difficult for sperm to reach and fertilize an egg, and by thinning the lining of the uterus to prevent implantation of a fertilized egg. It is important to note that Cerazette does not protect against sexually transmitted infections and should be taken consistently and at the same time every day to maintain its effectiveness. Women are advised to consult with their healthcare provider for personalized guidance on starting Cerazette.