Cholestagel may affect the way in which the following medicines work: • Anticoagulant therapy (medicines, such as warfarin, used to thin blood) • Thyroid replacement therapy (medicines, such as thyroxine or levothyroxine, used to treat low thyroid hormone levels) • Oral contraceptives (medicines to prevent pregnancy) It is important you take Cholestagel at least 4 hours after you take the oral contraceptive to ensure that the effectiveness of the contraceptive is not affected. • Verapamil (a medicine used to treat high blood pressure) • Antidiabetic medications (medicines, such as pioglitazone, repaglinide or glyburide used to treat diabetes) • Anti-epileptic medicines (medicines, such as phenytoin, used to treat epilepsy). • Ciclosporin (a medicine used to suppress the immune system).