Theoretically NSAIDs (including aspirin) might reduce the
efficacy of mifepristone, and combined use is often not recommended. However, evidence from two studies with
naproxen and diclofenac suggests no reduction in
mifepristone efficacy.
Because of theoretical concerns of antagonistic effects,
NSAID analgesics have been avoided in protocols for medical abortion. However, the limited available evidence suggests that this might not be necessary.