This invention relates to a pharmaceutical composition for mammals and, more particularly, to a pharmaceutical composition which enhances the action of an anaesthetic used in both human and veterinary applications, which, at least partly, reduces the risk of respiratory depression and enhances pulmonary perfusion. The pharmaceutical composition is characterized in that it contains a serotonergic ligand or any pharmacologically acceptable salt or ester thereof which acts on at least one member of the 5-HT family of serotonergic receptors, preferably on one or more of the 5-HTiA, 5-HT4 and 5-HT7 serotonergic receptors. In an example the ligand is the 8-OH-DPAT ligand. The composition can be used in conjunction with or include an anaesthetic, preferably an opioid anaesthetic, to induce a state of anaesthesia in mammals and it can be used to immobilize wile or non-domestic mammals.