Upset Stomach

• Some people experience upset stomach or nausea when taking red clover leaf extract.
  
  

Hormone Drug Interactions

• Because it acts similarly to estrogen, red clover leaf may interact with estrogen or progesterone and increase their effects. It also may decrease the effectiveness of birth control pills.
  
  

Blood Thinning

• Red clover leaf also may increase the effects of anti-coagulants such as warfarin, so people on blood thinners should avoid taking red clover leaf. People who have had a stroke, or who have a blood clotting disorder or other cardiovascular disease, also should not take red clover leaf.
  
  

Hormonal Considerations

• People should not take red clover leaf if they have a history of hormone-related cancer, such as cervical or ovarian cancer.
  
  

Allergic Reaction

• Rarely, people have a severe allergic reaction to red clover leaf. Signs include a rash or hives, difficulty breathing, chest tightness, and facial or mouth swelling.