The primary mechanism of action of progestogen-only<unk>  contraceptive pills is to prevent fertilization by inhibition of ovulation.LevonorgestrelMechanism and efficacy There is strong evidence that treatment with<unk>  acts primarily by preventing or delaying ovulation and by preventing fertilization.22–26 Studies have indicated that<unk>  does not prevent implantation.27–29 Experiments in monkeys and rats could detect no effect of a high dose of levonorgesterel administered postcoitally once fertilization had occurred.30,31 The evidence indicates that a postfertilization effect does not contribute to the efficacy of<unk> .25,30–33 Clinicians, pharmacists, and patients can be reassured that treatment with<unk>  is not an abortifacient.p. 157:The use of progesterone receptor modulators for<unk>  Mifepristone. In randomized trials, 10 mg mifepristone was as effective as 25, 50, or 600 mg. preventing about 80-85% of expected pregnancies (the same efficacy and side effects as with the levonorgestrel method), with a slight decrease in efficacy when treatment was delayed to 5 days after intercourse.16,52–54Ulipristal Acetate. Ulipristal acetate (ellaOne) has similar biologic effects as mifepristone and is approved for<unk>  in Europe and is expected to become available in the U.S.in a single oral dose of 30 mg. Randomized trials demonstrated that ulipristal acetate is slightly more effective than the single 1.5 mg dose of levonorgestrel when used within 72 hours after sexual intercourse and even between 72 h and 120h.55,56 … Progesterone receptor modulators like ulipristal acetate and mifepristone suppress ovarian follicular growth and also delay endometrial maturation, manifested in a delay in menstruation after treatment. Ovulation can be temporarily postponed.Other methodsAnother method of<unk>  is the insertion of a copper IUD, anytime during the preovulatory phase of the menstrual cycle and up to 5 days after ovulation. The failure rate (in a small number of studies) is very low, 0.1%.34,35 This method definitely prevents implantation, but it is not suitable for women who are not candidates for intrauterine contraception, e.g., multiple sexual partners or a rape victim. The use of a copper IUD for<unk>  is expensive, but not if it is retained as an ongoing method of contraception.It is believed that the main mechanism of action of high-dose progestin<unk>  is inhibition of ovulation, but other mechanisms may be involved... Taken together, these data are highly supportive of the concept that levonorgestrel<unk>  has little or no effect on postovulation events but is highly effective when taken before ovulation. Levonorgestrel<unk>  does not affect implantation and is not abortifacient.Intrauterine insertion of a copper IUD within 5 to 10 days of midcycle coitus is a very effective method of preventing continuation of the pregnancy… The LNG-IUS should not be used for<unk> .A study by the WHO reported that use of a single tablet of 10 mg of mifepristone was an effective<unk>  contraceptive with a pregnancy rate of 1.2%.Ulipristal, also known as CDB-2914, has been studied as an<unk>  contraceptive pill… In 2009, European regulatory approval was granted for a 30-mg tablet of ulipristal (under the brand name of EllaOne) as an<unk>  contraceptive pill for use up to 5 days after unprotected intercourse. An application for approval in the United States is under review. The best available evidence is that they do not have any post-fertilization effects such as the prevention of implantation. The U.S. FDA-approved labels and European EMA-approved labels (except for HRA Pharma's NorLevo) levonorgestrel<unk>  contraceptive pills (based on labels for regular oral contraceptive pills) say they may cause endometrial changes that discourage implantation. Daily use of regular oral contraceptive pills can alter the endometrium (although this has not been proven to interfere with implantation), but the isolated use of a levonorgestrel<unk>  contraceptive pill does not have time to alter the endometrium. In March 2011, the International Federation of Gynecology and Obstetrics (FIGO) issued a statement that: "review of the evidence suggests that LNG levonorgestreol<unk> Ps cannot prevent implantation of a fertilized egg. Language on implantation should not be included in LNG<unk> P product labeling."• Interfere with the process of ovulation;• May possibly prevent the sperm and the egg from meeting.Implications of the research:• Inhibition or delay of ovulation is LNG<unk> Ps principal and possibly the only mechanism of action.• Review of the evidence suggests that LNG<unk> Ps cannot prevent the implantation of a fertilized egg. Language on implantation should not be included in LNG<unk> P product labeling.• The fact that LNG<unk> Ps have no demonstrated effect on implantation explains why they are not 100% effective in preventing pregnancy and are less effective the later they are taken. Women should be given a clear message that LNG<unk> Ps are more effective the sooner they are taken.• LNG<unk> Ps do not interrupt a pregnancy (by any definition of the beginning of pregnancy). However, LNG<unk> Ps can prevent abortions by reducing unwanted pregnancies. In June 2012, a New York Times editorial called on the FDA to remove from the label the unsupported suggestion that levonorgestrel<unk>  contraceptive pills inhibit implantation. In November 2013, the European Medicines Agency (EMA) approved a change to the label for HRA Pharma's NorLevo saying it cannot prevent implantation of a fertilized egg. Progestogen-only<unk>  contraceptive does not appear to affect the function of the Fallopian tubes or increase the rate of<unk> topic pregnancies. The primary mechanism of action of progesterone receptor modulator<unk>  contraceptive pills like low-dose and mid-dose mifepristone and ulipristal acetate is to prevent fertilization by inhibition or delay of ovulation. One clinical study found that post-ovulatory administration of ulipristal acetate altered the endometrium, but whether the changes would inhibit implantation is unknown. The European EMA-approved labels for ulipristal acetate<unk>  contraceptive pills do not mention an effect on implantation, but the U.S. FDA-approved label says: "alterations to the endometrium that may affect implantation may also contribute to efficacy." The primary mechanism of action of copper-releasing intrauterine devices (IUDs) as<unk>  contraceptives is to prevent fertilization because of copper toxicity to sperm and ova. The very high effectiveness of copper-releasing IUDs as<unk>  contraceptives implies that they must also prevent some pregnancies by post-fertilization effects such as prevention of implantation.
Emergency contraception
Heat-based contraception
Long-acting reversible contraception
Male contraceptive
Menstrual extraction
Combined oral contraceptive pill
Combined hormonal contraception
Extended cycle combined hormonal contraceptive