Compounds of formula (I) and pharmaceutically acceptable salts thereof in which m is 0, 1 or 2; n is 2, 3, 4 or 5; X is carbonyl or a group of formula (II) in which R₅ is H or alkyl; Y is an alkylene chain optionally substituted by one or more alkyl groups; Z is an alkylene chain containing 2 to 5 carbon atoms optionally substituted by one or more alkyl groups; R is phenyl optionally substituted by one or more halo substituents or R is naphthyl; and R₁ and R₂, which are the same or different, are H, alkyl, or arylalkyl, provided that when R₁ is benzyl, R₂ is H or methyl; have utility in the treatment of drug misuse or other addictive disorders.