This week the Canadian Press reports that it may be dangerous to combine herbal supplements with heart medication.

Dr. Beth Abramson, a heart specialist at St. Michael’s Hospital in Toronto , tells CP that St. John’s wort can interfere with prescription medications like digoxin and warfarin — used to prevent blood clots — and that hawthorne can also be detrimental to people who take heart drugs. According to Abramson, even vitamin E can affect warafin as its anticoagulant properties can thin the blood too much.