Yes, a woman with a prior history of blood clot can safely take Plan B (levonorgestrel) emergency contraception.
Plan B is a progestin-only emergency contraceptive that does not increase thrombotic risk and is safe for women with a history of venous thromboembolism (VTE). This is a critical distinction from combined hormonal contraceptives (which contain estrogen) that are contraindicated in women with prior blood clots.
Key Evidence Supporting Safety
Progestin-Only Formulations Do Not Increase Clot Risk
The French Society of Endocrinology guidelines specifically note that levonorgestrel-based emergency contraception showed no excess risk of venous thromboembolism 1. The evidence demonstrates:
- No significant increase in VTE risk with levonorgestrel at emergency contraceptive doses (OR: 1.45 [95% CI: 0.92-2.26] for progestin-only methods overall, with no excess risk specifically noted for levonorgestrel 30 mg) 1
- Progestins at these doses do not affect hemostatic parameters 1
No Effect on Clotting Factors
A dedicated study examining clotting factors after emergency contraception found no obvious effect on Factor VII or antithrombin III levels after the Yuzpe regimen (which contains both estrogen and progestin). The study concluded that the short-lived dosage should not be automatically dismissed even in women with previous thromboembolic disease 2.
Broader Safety Profile
Research confirms that progestin-only contraceptives are generally considered safe for women at high risk for thrombosis, including those with a history of VTE 3. A systematic review found that most adverse reactions to levonorgestrel emergency contraception were common and not serious 4.
Critical Distinction: Emergency vs. Regular Contraception
Plan B is fundamentally different from regular hormonal contraception:
- Single-use, short duration: Contains only 1.5 mg total levonorgestrel taken once or in two 0.75 mg doses 12 hours apart 5
- No estrogen component: Unlike combined oral contraceptives that significantly increase VTE risk (2-4 fold), Plan B contains only progestin 1
- Brief exposure: The hormone exposure is extremely limited compared to ongoing contraceptive use
Important Caveats
What Plan B Does NOT Do:
- Does not protect against HIV/STIs 5
- Not intended for routine contraceptive use 5
- Not effective if already pregnant 5
When to Seek Medical Attention:
- Severe lower abdominal pain 3-5 weeks after taking Plan B (to evaluate for ectopic pregnancy) 5
- Period delayed more than one week beyond expected date 5
Practical Guidance
For a woman with prior VTE who needs emergency contraception:
- Plan B is safe to use - the progestin-only formulation does not increase thrombotic risk
- Take as soon as possible within 72 hours of unprotected intercourse for maximum efficacy 5
- No special monitoring required for the history of blood clot
- Continue anticoagulation if currently prescribed (levonorgestrel does not interact with anticoagulants) 6
The evidence is reassuring that the brief, progestin-only exposure from Plan B does not pose a thrombotic risk, even in women with previous blood clots. This is in stark contrast to estrogen-containing contraceptives, which are absolutely contraindicated in this population.