Plan B with blood thinners (warfarin, DOACs, heparin)
Many adults on chronic medications also take an anticoagulant — warfarin, a DOAC such as apixaban or rivaroxaban, or in hospital settings heparin. The combination with Plan B (Levonorgestrel) is common and most pairs are safe with appropriate monitoring, but a few specific interactions matter and should not be assumed away at 1.5mg.
How Plan B interacts with anticoagulants
Anticoagulants reduce blood clotting; medications that further affect platelet function or warfarin metabolism can amplify bleeding risk. Levonorgestrel interaction depends on whether the medication shares warfarin's CYP2C9 pathway, affects platelet function, or has its own bleeding risk. Plan B's primary mechanism is delaying or preventing ovulation when taken before the LH surge.
Practical guidance
According to the prescribing information for Levonorgestrel, anyone on chronic anticoagulation should review the addition of Plan B at 1.5mg with the prescriber or anticoagulation clinic. For warfarin, INR may need closer monitoring during the first weeks. For DOACs, fixed dosing and the absence of routine monitoring make the prescriber consultation more important rather than less.
Frequently asked questions
Can I take Plan B with warfarin? ▾
Most users can take Plan B with warfarin under monitoring at 1.5mg, but the combination warrants closer INR checks in the first weeks. Specific interactions of Levonorgestrel with warfarin are listed in the prescribing information; the anticoagulation clinic confirms the right approach.
Is Plan B safe on a DOAC like apixaban or rivaroxaban? ▾
For most DOAC users at 1.5mg, Plan B is acceptable. DOACs have specific interactions with strong CYP3A4 inhibitors and inducers; whether Levonorgestrel affects this pathway determines whether dose adjustment or alternative selection is needed. Pharmacist review is the practical safeguard.
More on Plan B
- With alcoholPlan B and alcohol — is it safe to drink?
- With foodShould Plan B be taken with food?
- Side effectsPlan B side effects: common, rare and warning signs
- Dosage guidePlan B dosage guide: how much to take and when
- OnsetHow fast does Plan B start working?
- DurationHow long does Plan B last?
The information on this website is provided for reference and educational purposes only. It does not replace consultation with a qualified healthcare professional.