The effectiveness of interferon for treating multiple sclerosis and other demyelinating diseases is synergistically potentiated by concomitant administration of a compound of Formula (I): wherein R1 is H, alkyl or OH, R2 is hydroxyalkyl or alkyl-O-L1, R3 is H or OH, X is C(═CH2), CH(OH), or spirooxirane-2, Z is CH2CH(OH) or C(=0), and R4 is an optionally substituted L2-alkyl or L2-alkenyl, wherein L2 is an optionally substituted 3-furanyl or 3-fur-3-enyl moiety.