Enzyme-inducing drugs (such as carbamazepine), which increase the
metabolism of contraceptive steroids, may reduce the
efficacy of
HRT.
This effect is most noticeable where
HRT is prescribed for menopausal vasomotor
symptoms, but might be difficult to detect where the indication is osteoporosis. Any interaction may be less likely with transdermal
HRT. However, as yet the
clinical significance of any interaction is unclear.