Progestin-Only Pills: Available Formulations
The progestin-only pills currently available in the United States include norethindrone (or norethindrone acetate), norgestrel, and drospirenone formulations. 1
Specific Formulations
Traditional Progestin-Only Pills
- Norethindrone-containing pills: These are the most commonly prescribed traditional progestin-only pills in the U.S., available as norethindrone or norethindrone acetate formulations 2
- Norgestrel pills (Ovrette): Another traditional formulation, though less commonly used 2
- Levonorgestrel 30 μg: This formulation has been studied extensively, though specific brand availability may vary 3
Newer-Generation Progestin-Only Pills
- Drospirenone 4 mg (24/4 regimen): This is a newer-generation progestin-only pill that differs significantly from traditional formulations, containing 24 active tablets followed by 4 placebo tablets 1, 4
- Desogestrel 75 μg (Cerazette): While widely available in Europe, this formulation's U.S. availability is limited 3
Key Distinctions Between Formulations
Timing Requirements
The different progestin-only pills have varying backup contraception requirements when starting 1:
- Norethindrone or norgestrel: Require backup contraception for 2 days if started more than 5 days after menses began 1
- Drospirenone: Requires backup contraception for 7 days if started more than 1 day after menses began 1
Mechanism of Action
Traditional progestin-only pills (norethindrone, norgestrel, levonorgestrel) primarily work by thickening cervical mucus rather than consistently inhibiting ovulation 5. In contrast, newer formulations like drospirenone and desogestrel more reliably inhibit ovulation, making them closer to combined oral contraceptives in mechanism 5, 4.
Clinical Considerations for a 40-Year-Old Woman
For a healthy 40-year-old woman with no contraindications, any of these formulations would be medically appropriate 1. The choice depends on:
- Preference for daily timing flexibility: Drospirenone offers a 24-hour "safety window" for missed pills, unlike traditional formulations that require strict timing 4
- Bleeding pattern tolerance: Traditional pills may cause more irregular bleeding initially, while drospirenone users experience more predictable patterns due to the 4-day hormone-free interval 4
- Antiandrogenic benefits: Drospirenone has antiandrogenic properties that may benefit women with hyperandrogenic features 6
Efficacy Considerations
The median Pearl Index for traditional progestin-only pills during typical use is approximately 2.0, with perfect use rates around 1.05 5. Desogestrel and drospirenone formulations demonstrate superior contraceptive efficacy, with desogestrel showing a Pearl Index of 0.14 compared to levonorgestrel's 1.17 3.