Reduced anticoagulant effect w/ anticoagulants. Decreased effect & increased level of aspirin in the blood (up to toxic levels) w/ aspirin. Prolonged barbiturate effect. Increased risk of pregnancy w/ birth control pills. Induced tissue desaturation of ascorbic acid w/ aspirin, nicotine, alcohol, appetite suppressants, Fe, phenytoin, anticonvulsants, estrogen & OC & tetracycline.