Hello, Thank you for writing to HCM about your query, Brief Answer - Headache, Dizziness and Slow Heartbeat are the common side effects for estroven. Explained Answer - The side effects Dangerous Effects According to the University of Maryland Medical Center, black cohosh contains sugar compounds called glycosides; isoferulic acids, Which have anti-inflammatory effects; and plant-based estrogens, or phytoestrogens. Phytoestrogens have a similar structure to estrogen, and are thought to mimic its effects on the body. The soy isoflavones contained in Estroven are also phytoestrogens, so those who have had hormone-receptive breast, ovarian or cervical cancer should only take Estroven under a physician s supervision. Liver toxicity has been reported with high doses of black cohosh, but a direct link has not been established. Estroven should be taken only as directed and anyone experiencing yellowing of the skin and eyes should contact physician immediately. Hope above information will help you out. Thanks & Regards, Dr. Gaurav Prajapati