Several substances can interfere with the accuracy of fecal occult blood test results. Most kits require that users avoid consuming red meat (beef, lamb, or liver in any form) or vitamin C in excess of 250 mg per day for three days prior to and during the stool collection. Nonsteroidal anti-inflammatory drugs--such as ibuprofen, naproxen, or more than one adult aspirin per day--should often be avoided for seven days before and during the test period.