Hello, Since taking prehern / agnus castus possibly will interfere with the efficacy of Microgynon that you have been taking, you should ideally stop taking the herbs. If you are not ready for pregnancy, take the CP as directed in the leaflet to get the best efficacy. Forgetting to take the CP in the right time everyday, taking other medicines or herbs that will affect its efficacy, or skipping it every now and then may put you at risk of getting pregnant. If you want to use some other contraceptive method then you should use it as long as you are taking the herbs. Contraceptive pills and methods, will protect you from getting pregnant but not from sexually transmitted diseases. Always use condoms to practice safe sex apart from whatever contraception method you might be using. Stay away from smoking, alcohol, drugs etc., for the best efficacy of CP and protection against pregnancy. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Nupur K., General & Family Physician