Can Slynd Cause Blood Clots?
Slynd (drospirenone 4 mg progestin-only pill) does not appear to increase the risk of blood clots, unlike combined oral contraceptives containing drospirenone plus estrogen, which do carry an elevated venous thromboembolism risk. 1
Critical Distinction: Progestin-Only vs. Combined Formulations
The thrombotic risk profile of drospirenone depends entirely on whether it is combined with estrogen:
Slynd (Drospirenone-Only Pill)
- Contains 4 mg drospirenone without any estrogen 1
- No cases of deep vein thrombosis or pulmonary embolism were reported in Phase III trials involving 1,571 women across 14,329 exposure cycles 1
- Progestin-only pills generally do not increase the risk of venous thromboembolism, stroke, or myocardial infarction 1
- This formulation provides contraceptive efficacy similar to combined oral contraceptives but with a favorable safety profile regarding thrombotic events 1
Combined Drospirenone/Ethinyl Estradiol Pills (Yaz, Yasmin, etc.)
- These DO carry an increased risk of venous thromboembolism compared to other combined oral contraceptives 2, 3
- The VTE risk with drospirenone-containing combined oral contraceptives is approximately 10 per 10,000 woman-years, compared to 3-9 per 10,000 woman-years for standard combined oral contraceptives and 1-5 per 10,000 woman-years for non-users 2
- Drospirenone combined with ethinyl estradiol shows a 50-80% higher relative risk of venous thrombosis compared to levonorgestrel-containing combined oral contraceptives 2
- Multiple studies confirm this elevated risk: the hazard ratio for venous thromboembolism with drospirenone/ethinyl estradiol is 1.77 (95% CI 1.33-2.35) compared to low-dose estrogen comparators 4
Why the Difference Matters
The estrogen component, not the drospirenone progestin, is primarily responsible for the increased thrombotic risk in combined oral contraceptives:
- All combined oral contraceptives increase VTE risk due to their estrogen content 2, 3
- The specific progestin type (including drospirenone) modulates this baseline estrogen-related risk 2
- Progestin-only formulations like Slynd avoid this estrogen-mediated thrombotic pathway entirely 1
FDA Labeling and Warnings
The FDA label for combined drospirenone/ethinyl estradiol products explicitly warns about increased blood clot risk, stating that women using birth control pills with drospirenone may have a higher risk of getting a blood clot compared to pills without drospirenone 3. This warning applies specifically to the combined formulations, not to Slynd.
The FDA label lists as serious risks:
- Deep vein thrombosis in the legs 3
- Pulmonary embolism in the lungs 3
- Blood clots in the eyes causing vision loss 3
- Heart attack and stroke 3
Clinical Bottom Line
For patients concerned about clot risk, Slynd represents a safer drospirenone option because it lacks the estrogen component that drives thrombotic complications in combined oral contraceptives 1. The Phase III safety data showing zero thromboembolic events across substantial exposure provides reassuring evidence 1.
However, patients switching from combined drospirenone pills to Slynd should understand they are choosing a fundamentally different medication class with distinct contraceptive mechanisms and bleeding patterns, not simply a lower-risk version of the same drug 1.