The hormones in
HRT are similar to those used in oral
contraceptives, and so may be affected by enzyme-inducing drugs in the same way as
contraceptives. Reduced effects are therefore possible if
phenytoin or fosphenytoin is also given.
Any interaction would be most likely to be noticed where
HRT is prescribed for menopausal vasomotor
symptoms. Further study is needed to confirm the importance of this possible interaction.