Background and Objective: The beneficial effects of Ephedra Major in treating hypertension, common cold and muscle weakness have been reported. As there are no previous studies that assess its effects during pregnancy, we aimed to assess the biological effects of Ephedra Major extract on the quantitative development of Balb/C mouse embryos during the third to sixth days of pregnancy

Materials and Methods: In this study, 50 female Balb/C mice were randomly divided into 6 equal groups consisting of a control group (no injection), a sham group (injection of saline) and 4 experimental groups. The in vivo LD50 was determined as 3086 mg/kg and the injection doses were chosen at 300 and 500 mg/kg. Injection was done on the third to sixth days by enema. Then the mice were dissected on the 15th day of pregnancy. The experiment was performed twice. Data were analyzed by Duncan test in SPSS21.  P<0/001 was considered statistical significance.

Results: All embryos were atrophied in the group receiving 500 mg/kg Ephedra Major. We observed reduced myometrial thickness and disruption in the natural order of the endometrial layer. In the group receiving 300mg/kg, a significant decrease (P<0/001) in the Crown–Rump Length (CR), embryo weight and placental weight was noted compared with other groups.

Conclusion: According to our observations, it seems that using this herb during pregnancy is hazardous. In addition to abortion, it may have a negative effect on embryonic development.