What is Micronor (norethindrone), a form of oral contraceptive?

From the Guidelines

Micronor, a progestin-only pill, is a suitable option for women who cannot use estrogen-containing contraceptives, and it should be taken at the same time every day to maintain its effectiveness, as supported by the most recent guidelines 1.

Key Points to Consider

• Micronor contains norethindrone 0.35 mg and works by thickening cervical mucus to block sperm and sometimes preventing ovulation.
• It is approximately 91-95% effective with perfect use, but its effectiveness may be lower with typical use, as noted in studies on contraceptive efficacy 1.
• Common side effects include irregular bleeding patterns, spotting, headaches, breast tenderness, and mood changes.
• Micronor is suitable for breastfeeding women, smokers over 35, and those with certain cardiovascular risk factors because it does not contain estrogen.

Initiation and Use

• According to the U.S. selected practice recommendations for contraceptive use, 2024, progestin-only pills like Micronor can be started at any time, with the consideration of using backup contraception for 2 days if started more than 5 days after menses began 1.
• If a pill is missed by more than 3 hours, it should be taken immediately, and backup contraception should be used for 48 hours.

Comparison with Other Contraceptives

• The effectiveness and side effects of Micronor are comparable to other progestin-only pills, but it offers continuous protection without the need for a 7-day break, as seen with combined hormonal contraceptives.
• The choice between Micronor and other contraceptives should be based on individual patient needs, medical history, and preferences, considering the latest guidelines and recommendations 1.

From the FDA Drug Label

CLINICAL PHARMACOLOGY 1. Mode of Action Norethindrone tablets progestin-only oral contraceptives prevent conception by suppressing ovulation in approximately half of users, thickening the cervical mucus to inhibit sperm penetration, lowering the mid-cycle LH and FSH peaks, slowing the movement of the ovum through the fallopian tubes, and altering the endometrium. The primary mechanism of action of Micronor (Norethindrone) is to prevent conception by:

• Suppressing ovulation in approximately half of users
• Thickening the cervical mucus to inhibit sperm penetration
• Lowering the mid-cycle LH and FSH peaks
• Slowing the movement of the ovum through the fallopian tubes
• Altering the endometrium 2

From the Research

Overview of Micronor

• Micronor is a progestin-only pill, a type of contraceptive method 3.
• It is one of the progestin-only contraceptives (POCs) available in the United States, along with Ovrette, depot medroxyprogesterone acetate (DMPA) injections, levonorgestrel intrauterine system (IUS), and etonogestrel implant 3.

Characteristics and Use

• Micronor is a daily progestin-only pill, which has specific advantages and drawbacks 3.
• The use of Micronor and other POCs requires adequate and accurate information, as well as detailed counseling, to improve the likelihood of adherence and continuation 3.
• Progestin-only contraceptives, such as Micronor, may be preferable in situations where there are absolute or relative contraindications to estrogen, side-effects to estrogen-containing hormonal contraception, lactation, and comfort and feasibility of formulations for long-term use 4.

Effectiveness and Safety

• The effectiveness of Micronor and other contraceptive methods is determined by a combination of drug or device efficacy, individual fecundability, coital frequency, and user adherence and continuation 5.
• Progestin-only methods, such as Micronor, are associated with rare serious risks, and hormonal contraceptives can improve medical conditions associated with hormonal changes related to the menstrual cycle 5.
• Optimal contraceptive selection requires patient and clinician discussion of the patient's tolerance for risk of pregnancy, menstrual bleeding changes, other risks, and personal values and preferences 5.