some information which i found from online on Dang Gui :
Dong Quai (Angelica sinensis, Dang Gui, Tang-kuei) grows profusely throughout Asia. Called the "female ginseng" dong quai is an all-purpose herb for a wide range of female gynecological complaints. For centuries, Chinese women have used this herb to regulate the menstrual cycle and quell painful menstrual cramps caused by uterine contractions. Modern herbalists use dong quai to eliminate the discomfort of premenstrual syndrome PMS and to help women resume normal menstruation after going off "the pill." Dong quai is also reputed to be useful against hot flashes and other symptoms of menopause caused by hormonal changes. Rich in vitamins and minerals including A, B12, and E, this herb may also prevent anemia. Dong quai has also been used to treat insomnia and high blood pressure for both sexes. Both men and women use this herb as a blood tonic. One of the most widely used herbs in the Orient, Dong Quai Duck is a popular Cantonese dish.
In the Journal of Natural Products (45:398, 1982) it says that Dong Quai, Angelica sinensis has been used as an antispasmodic, a blood purifier, and to help hypertension, rheumatism, ulcers, anemia, and constipation.
Dong Quai also contains compounds that act to stimulate the central nervous system, supporting its use as a mild energizer for people.
Researchers have identified several coumarin derivatives that are known to act as antispasmodics and vasodilators. Dong quai, Angelica sinensis key ingredients include Ligustilide, butylene phthalide and butyl phthalide found in the aromatic oil. Ferulic acid and various polysaccharides are found in the non-aromatic fractions. Research suggests that both ferulic acid and ligustilide are responsible for preventing spasms, relaxing blood vessels and reducing blood clotting in peripheral vessels.
Caution: Do not use Dong Quai, Dang Gui during pregnancy or if you are still menstruating and typically have a heavy flow.