The anticoagulant effects of dicoumarol and phenprocoumon can be decreased, and those of acenocoumarol increased, by hormonal
contraceptives. An isolated report describes a marked INR increase in a woman taking
warfarin when she was given levonorgestrel emergency contraception. A report describes a woman who needed more acenocoumarol when her
HRT treatment with oral conjugated oestrogens was changed to transdermal
estradiol.
Direct information is limited. Combined hormonal
contraceptives are usually contraindicated in patients with thromboembolic disorders. However, if they are used be aware that the anticoagulant response may be affected.