Is Norethindrone a Progestin-Only Contraceptive?
Yes, norethindrone is available as a progestin-only contraceptive (POP), though it is also used in combination with estrogen in combined oral contraceptives (COCs).
Norethindrone Formulations
Norethindrone exists in two distinct contraceptive formulations:
Progestin-Only Pills (POPs)
- Norethindrone 0.35 mg tablets are progestin-only oral contraceptives that provide continuous daily dosing without any estrogen component 1
- These progestin-only pills work by suppressing ovulation in approximately half of users, thickening cervical mucus to inhibit sperm penetration, lowering mid-cycle LH and FSH peaks, slowing ovum movement through fallopian tubes, and altering the endometrium 1
- Progestin-only formulations containing norethindrone (first generation) or drospirenone (fourth generation) are available for contraceptive purposes 2
Combined Oral Contraceptives (COCs)
- Norethindrone is also used as the progestin component in combination pills that contain ethinyl estradiol 2
- These combination formulations typically contain 500-1000 micrograms of norethindrone with 30-40 micrograms of ethinyl estradiol 3
- Norethindrone acetate is used in combination pills like Estrostep Fe, which are FDA-approved for acne treatment due to moderate antiandrogenic effects 4
Clinical Characteristics of Norethindrone
Classification and Properties
- Norethindrone is classified as a first-generation progestin that was originally used in high doses with potent off-target effects on androgen and glucocorticoid receptors 2
- As a first-generation progestin, it historically contributed to acne and adverse metabolic effects such as lower high-density lipoprotein levels when used in high doses 2
Metabolic Profile
- Progestin-only formulations of norethindrone have only minor metabolic effects compared to combination pills 3
- Low-dose norethindrone in combination formulations (500 micrograms) was associated with favorable lipid profiles, including a 10% increase in HDL cholesterol and a 12% reduction in LDL cholesterol 3
- Progestin-only formulations or combinations containing low-dose norethindrone were associated with the most favorable metabolic profiles among oral contraceptives studied 3
Side Effect Profile
- Progestin-only pills containing norethindrone are associated with irregular bleeding and require strict adherence, needing to be taken at the same time each day 2
- These characteristics have made combined hormonal contraceptives a more popular option in recent years 2
Important Clinical Distinction
The key point is that norethindrone can be either progestin-only OR combined with estrogen, depending on the specific formulation prescribed 2, 1. When prescribing or discussing norethindrone, always verify which formulation is being used, as the 0.35 mg dose specifically refers to the progestin-only preparation 1.