The present invention relates to compounds which include compounds of the formula I: or a pharmaceutically acceptable salt thereof, wherein one of R1 and R4 is selected from the group consisting of H, and optionally substituted C1-6 alkyl, C3-7 cycloalkyl, C3-7 cycloalkyl-C1-4 alkyl, and phenyl-C1-4 alkyl; and the other of R1 and R4 is an optionally substituted C9-14 aryl group; R2 and R3 are either: (i) independently selected from H, R, R′, SO2R, C(═O)R, (CH2)nNR5R6, where n is from 1 to 4 and R5 and R6 are independently selected from H and R, where R is optionally substituted C1-4 alkyl, and R′ is optionally substituted phenyl-C1-4 alkyl, or (ii) together with the nitrogen atom to which they are attached, form an optionally substituted C5-7 heterocyclic group. The compounds are useful in the treatment of conditions including conditions which can be alleviated by antagonism of a 5-HT2B receptor such as GI disorders and congestive heart failure.