Dong quai is usually not recommended by western physicians during pregnancy and for diabetics. It is also known to affect blood pressure, heart action, and respiration when taken at large doses. Potentially, it can react with sunlight to cause a rash or sunburn and may cause diarrhea or abdominal bloating. Also, menstrual bleeding may increase when taking dong quai.

The hemotinic, or blood tonic, effect of Dong quai is now attributed to its vitamin B12, folic acid, folinic acid, nicotinic acid and biotin contents. Dong quai is also rich in the metal cobalt, which is the major element responsible of vitamin B12's blood enriching action. Experiments have shown that once vitamin B12 loses 0.01 gram of cobalt, its blood enriching effect immediately disappears.

Pharmacological studies indicate that Dong quai have estrogenic action. Consequently, potentially negative effects of dong quai--such as breast cancer risk--can not be excluded. More long-term studies of dong quai are needed, to fully assess how it affects the body.

However, in recent studies involving postmenopausal women, dong quai proved to be no more effective than a placebo in relieving such common menopausal symptoms as hot flashes and vaginal dryness. In one study, the herb and the placebo both reduced the frequency of hot flashes by 25% to 30%. This type of disappointing result may simply highlight the importance of taking dong quai in combination with other herbs.

Tip:
Dong quai is not recommended during pregnancy, for women with excessive menstrual flow or for people taking blood thinning agents.

Limit your exposure to the sun when taking dong quai, especially if you are fair-skinned; it contains substances called psoralens that can react with sunlight to cause a rash or severe sunburn. If you experience one of these effects or photosensitivity, stop taking dong quai.