Reversible benefit of estrogen replacement therapy

Bone mineral content in postmenopausal women during three years of treatment: the first two years with either placebo (red) or with estradiol cyclically combined with a small dose of norethisterone (blue); the women were then re-randomized to continued therapy or the other regimen in the third year. Estrogen therapy increased bone density when given as initial therapy (upper curve) and after two years of placebo. Replacement of estrogen with placebo led to a decline in bone density.