Birth control pills work by suppressing ovulation, changing cervical mucus, or other methods to achieve contraception. However, oral contraceptives need to be taken correctly in order to achieve the goal of protecting women from pregnancy, and it is not easy to say if you miss the time to take the pill. So, when is the pill effective? Here, take a look. Three commonly used birth control pills the correct way to take: 1, short-acting contraceptive pill The main components are progestin and estrogen. It has the effect of inhibiting ovulation, hindering the normal growth of the endometrium, changing the nature of cervical mucus and changing the normal peristalsis of the fallopian tubes. It is suitable for women who do not have underlying diseases or diabetes. Start taking the pill on the 5th day from the day of menstruation, and take 1 tablet every night for 22 days to prevent pregnancy for 1 month. 2, emergency contraceptive pill The main component is progestin. The principle of action of the drug is basically the same as the short-acting contraceptive pill. Suitable for women under 40 years old. There are mainly Yuktin, Noxal, Bostin and Mifepristone tablets. Generally, the first tablet is taken within 72 hours after intercourse, and then 1 tablet after 12 hours, the earlier you take it, the better the effect. 3.Long-acting contraceptive pill Generally after the onset of menstruation, the fifth day to take 1 tablet, 20 days later to take 1 tablet. Contains synthetic progestin and long-acting estrogen. After the drug enters the body, it will be stored in the fatty tissue, and later slowly released to inhibit ovulation and play a long-acting contraceptive role. It is suitable for women who cannot have an IUD placed and do not want to use other contraceptive methods.