3,8-Dihydrodiligustilide is a nonsteroidal phytoprogestogen that is found in Ligusticum chuanxiong. It is a potent agonist of the progesterone receptor (EC<sub>50</sub> = 90 nM). Another compound in the plant, riligustilide, is also a phytoprogestogen, but is almost 1,000-fold less potent and is very weak in comparison (EC<sub>50</sub> â 81 üM).