[1][2] It is a stereoisomer of the naturally occurring progestogen progesterone, in which the hydrogen atom at the 9th carbon is in the α-position (below the plane) instead of the β-position (above the plane) and the methyl group at the 10th carbon is in the β-position instead of the α-position.

[1][2] In other words, the atom positions at the two carbons have been reversed relative to progesterone, hence the name retroprogesterone.

This reversal results in a "bent" configuration in which the plane of rings A and B is orientated at a 60° angle below the rings C and D.[3] This configuration is ideal for interaction with the progesterone receptor, with retroprogesterone binding with high affinity to this receptor.

[4] However, the configuration is not as ideal for binding to other steroid hormone receptors, and as a result, retroprogesterone derivatives have increased selectivity for the progesterone receptor relative to progesterone.

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