A chemical compound of formula (I) wherein R.sub.1 and R.sub.2 are independently selected from hydrogen and alkyl; R.sub.3 is alkyl; R.sub.4 and R.sub.5 are selected from hydrogen and alkyl; R.sub.6 and R.sub.7 are independently selected from hydrogen, halogen, hydroxyl, alkyl, aryl, amino, alkylamino, dialkylamino, alkoxy, aryloxy, alkylthio, alkylsulfoxyl, nitro, carbonitrile, carbo-alkoxy, carbo-aryloxy and carboxyl; and A is a 5- or 6-membered ring optionally containing one or more heteroatoms wherein the atoms of the ring A, other than the unsaturated carbon atoms of the phenyl ring to which the ring A is fused, are saturated or unsaturated, and pharmaceutically acceptable salts, addition compounds and prodrugs thereof; and the use thereof in therapy, particularly as an agonist or antagonist of a 5HT receptor, particularly a 5HT.sub.2C receptor, for instance in the treatment of disorders of the central nervous system; damage to the central nervous system; cardiovascular disorders; gastrointestinal disorders; diabetes insipidus, and sleep apnea, and particularly for the treatment of obesity.