Unfortunately, folic acid can reduce the effectiveness of methotrexate. The medication works by interfering with folic acid, preventing embryonic cells from dividing and multiplying. If you consume a diet high in folates (including multi-vitamins), this may prevent the methotrexate from blocking enough activity to stop the ectopic embryo from growing. You need to return to your physician for a follow-up ultrasound and further testing to ensure the single dose was effective. You may need an additional dose of methotrexate or a different treatment to end the tubal pregnancy.