How can St John's wort affect the contraceptive efficacy of Nexplanon (etonogestrel)?

St John's wort may reduce Nexplanon (etonogestrel) contraceptive efficacy by inducing enzymes that increase hormone clearance, potentially causing contraceptive failure; implant removal is unnecessary, but an additional non-hormonal contraceptive method is advised during concurrent use and for 28 days after stopping St John's wort.