Calendula has potent muscle-relaxing properties and can cause a reaction when mixed with sedatives, diabetes medications, or blood pressure treatments. Pregnant and breastfeeding women should avoid ingesting calendula because the strong menstrual effects could lead to miscarriage or harm to the fetus. Also, if you're allergic to the Asteraceae or Compositae family of herbs -- including echinacea, ragweed, or chamomile -- then you should avoid taking calendula.

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