St. John’s wort is a popular dietary supplement that some people take to help relieve depression symptoms.

Scott Davis and his research colleagues at Wake Forest Baptist Medical Center found that nearly 30 percent of patients who take the supplement are also taking common medicines, including statins, blood thinners, selective serotonin reuptake inhibitors (SSRIs), digoxin, and benzodiazepines.

St. John’s wort can lower the effectiveness of these medications and lead to treatment failure.

Other potential results from bad supplement-drug combinations include heart abnormalities, unplanned pregnancy from contraceptive failure, and serotonin syndrome — a potentially life-threatening drug reaction.

Over-the-counter medications and supplements like St. John’s wort are not as closely regulated as prescription drugs, and many patients don’t tell their doctors about the supplements they are taking.

Inform your doctor of all medicines, including over-the-counter drugs and supplements, that you are taking.