 The affinity of dydrogesterone for the PR is relatively low at about 16% of that of progesterone.However, "in vivo", dydrogesterone is comparatively much more potent by the oral route, with an equivalent dose, in terms of endometrial proliferation, that is 10 to 20 times lower than that of progesterone.This is due to pharmacokinetic differences between the two medications, namely improved bioavailability and metabolic stability with dydrogesterone as well as additional progestogenic activity of its metabolites.