A new analysis of data from the Women's Health Initiative (WHI) suggests that, for older women taking estrogen-only HRT, rises in stroke risk and falls in fracture risk stop when treatment is discontinued.
However, the reduced risk of breast cancer among these women continues after treatment stops, data show.
The WHI study was a placebo-controlled, randomised trial of conjugated equine estrogen-only therapy (CEE). It involved 10,739 postmenopausal women aged 50 to 79 years who had had hysterectomies.
The trial was stopped one year early because of an increased risk of stroke among women in the treatment arm of the study.
The new analysis showed that this increased risk dissipated once treatment ceased, but that some benefits stopped as well.
The researchers said the findings highlighted the need to counsel women differently depending on their age and hysterectomy status.
They said: 'A postmenopausal woman who has had a hysterectomy and is considering initiation of CEE should be counselled about the risks of venous thromboembolism and stroke during treatment, which diminish with treatment cessation.
'Among younger women, no new safety concerns emerged and some risk reductions became apparent.'
They added: 'Among older women, risks of colorectal cancer and the global index of chronic diseases were elevated over the cumulative follow-up period.'
However, the researchers said risks and benefits of treatment for longer than six years could not be inferred from their data.