Supplements containing St. John's wort may interfere with birth control, antidepressants, blood thinners and other drugs, a U.S. non-profit group says. Senior nutritionist David Schardt of the Center for Science in the Public Interest in Washington requested the U.S. Food and Drug Administration to require a warning label on products containing St. John's wort -- a flowering plant often promoted for its supposed antidepressant properties. People who take the supplement with prescription antidepressants may unwittingly be counteracting the very treatment they are seeking, and women taking St. John's wort and oral contraceptives may have unplanned pregnancies, Schardt explained. "Consumers take St. John's wort and other herbal supplements based on their belief that they will benefit in some way, and perhaps some will," Schardt said in a statement. "But all consumers need to know that St. John's wort and many commonly prescribed drugs simply don't mix." The CSPI petition suggests the following warning label: "CAUTION: St. John's wort interacts with some commonly used prescription and over-the-counter drugs. DO NOT USE this supplement if you are taking contraceptives, antidepressants, immunosuppressants (such as cyclosporine), anticoagulants, Digoxin, HIV medicine, blood thinners, seizure-control medicine, cancer medicine, or any other medications."