BACKGROUND: Endometriosis (EMS) is a relapsing and estrogen-dependent disease. For endometriosis such as deep endometriosis and ovarian endometrioid cysts, surgery is the most effective treatment. Long-term follow-up showed that the recurrence rate of endometriosis after surgical treatment was high, so postoperative drugs were needed to reduce recurrence, and Gonadotropin-releasing hormone agonists (GnRH-a) were the most commonly used drug for postoperative management.GnRH-a may reduce the post-treatment endometriosis relapses by lowering the hormone levels in the body. However, the use of GnRH-a can give rise to perimenopausal symptoms, especially osteoporosis, bone loss, and bone pain, for which reason GnRH-a use is often limited. The add-back therapy is often used to alleviate the untoward effects caused by GnRH-a. However, long-term use of hormone drugs may lead to EMS recurrence, thrombosis, and breast cancer. Therefore, a safer and more effective drug is urgently needed to alleviate the untoward effects caused by GnRH-a. In recent years, scholars at home and abroad have found that isopropanolic Cimicifuga racemosa extract (ICR), as a plant extract, can better relieve the symptoms of perimenopausal women. At the same time, some studies have initially confirmed that black cohosh preparations can relieve the perimenopausal symptoms caused by GnRH-a treatment in EMS patients. OBJECTIVE: To investigate the effect of black cohosh preparations on the bone metabolism of rat models with GnRH-a-induced perimenopausal symptoms. METHODS: The rat models of perimenopausal symptoms were established by GnRH-a injection. and normal saline (NS injection) was used as the control. According to the modeling method and drug intervention, the rats were randomly divided into four groups: GnRH-a injection + saline intervention group (GnRH-a + NS), saline injection control + saline intervention group (NS + NS), GnRH-a injection + estradiol intervention group (GnRH-a + E2), and GnRH-a injection + black cohosh preparation intervention group (GnRH-a + ICR). The rat models were identified with the vaginal smear method, and then the corresponding drug intervention was administrated for 28 days. After the intervention, the rats were sacrificed. The rats' bone mineral density (BMD) of the distal femur was detected by a dual-energy X-ray bone density scanner. Rat tibia bone tissues were decalcified and made into slices. The pathological and morphological changes of rat tibial bones in each group were observed through HE staining. Histomorphometry parameters of rat tibial bones in each group, such as trabecular bone volume (TBV), trabecular thickness (TbTh), trabecular number (TbN), and trabecular spacing (TbSp), were detected and analyzed by using an automatic image analysis system. RESULTS: (1) The BMD level of the distal femur in the GnRH-a + NS group was significantly lower than the NS + NS, GnRH-a + E2, and GnRH-a + ICR groups (<0.01), the BMD levels in GnRH-a + E2 and GnRH-a + ICR groups were slightly lower than the NS + NS group, but there was no significant difference among the three groups (>0.05). (2) The pathological changes of the tibia bones under the microscope in different groups were as follows: The tibia bone trabecular structure was normal in the NS + NS group, without trabecular thinning or fracture, and the arch structure was normal. In the GnRH-a + NS group, some trabecular structures tapered, the arch structure disappeared, but no obvious bone fracture was observed in the trabecula. In the GnRH-a + E2 and GnRH-a + ICR groups, the trabecular structures were normal, without trabecular bone thinning or fracture, and the arch structures were normal. (3) The TBV level of the GnRH-a + INS group was significantly lower than that of the NS + NS, GnRH-a + E2 and GnRH-a + ICR groups (<0.01, <0.05, <0.01), while there was no significant difference among NS + NS, GnRH-a + E2 and GnRH-a + ICR groups (>0.05). (4) The TbTh levels in the four groups had no significant difference (>0.05). Compared with the NS + NS group, the TbTh levels in the GnRH-a + NS, GnRH-a + E2, and GnRH-a + ICR groups showed a descending tendency, while the TbTh levels in the GnRH-a + E2 and GnRH-a + ICR groups were slightly higher than that of the GnRH-a + NS group. However, such differences were not significant statistically (P>0.05). (5) Compared with the NS + NS group, the TbN levels in the GnRH-a + NS, GnRH-a + E2, and GnRH-a + ICR groups decreased remarkably (<0.05). Compared with the GnRH-a + NS group, the TbN levels in the GnRH-a + E2 and GnRH-a + ICR groups showed a mild descending tendency, but such differences were not significant statistically (>0.05). (6) The TbSp level of the GnRH-a + NS group was significantly higher than that of the NS + NS, GnRH-a + E2, and GnRH-a + ICR groups (<0.01), while there was no significant difference among NS + NS, GnRH-a + E2 and GnRH-a + ICR groups (>0.05). CONCLUSION: The GnRH-a injection could achieve the desired effect. GnRH-a injection may lead to the loss of bone mass in rats. Black cohosh preparations, like estrogen, may have a protective effect on bone mass loss caused by GnRH-a injection.