The type of progestogen in combined menopausal hormone therapy may also modulate VTE risk. Oral estrogens plus dydrogesterone appears to have lower VTE risk relative to inclusion of other progestins. Norpregnane derivatives such as nomegestrol acetate and promegestone have been associated with a significantly greater risk of VTE than pregnane derivatives such as medroxyprogesterone acetate and dydrogesterone and nortestosterone derivatives such as norethisterone and levonorgestrel. However, these findings may just be statistical artifacts. In contrast to progestins, the addition of oral progesterone to either oral or transdermal estrogen therapy is not associated with a higher risk of VTE. However, oral progesterone achieves very low progesterone levels and has relatively weak progestogenic effects, which might be responsible for the absence of increase in VTE risk. Parenteral progesterone, such as vaginal or injectable progesterone, which can achieve luteal-phase levels of progesterone and associated progestogenic effects, has not been characterized in terms of VTE risk.