Violent behaviour towards others is occasionally caused by drug therapy, through sometimes complex and often poorly understood mechanisms. The consequences described in detailed case reports can be serious, including homicide. Many neuropsychotropic drugs can induce violent behaviour: smoking cessation drugs, selective serotonin reuptake inhibitor antidepressants, amphetamines, benzodiazepines and dopamine agonists. Some drugs not used as psychotropic agents have also been implicated, for example: corticosteroids; anti-infective drugs such as mefloquine, efavirenz, atazanavir, ribavirin and alfa interferons; testosterone; and the asthma drug montelukast. The frequency of these adverse effects cannot be reliably assessed using the data available. Only certain reports mention a previous behaviour disorder. In practice, it is helpful to inform patients if the drugs they are taking can provoke violent behaviour. It is advisable to ask these patients about any behavioural changes and to encourage them to inform members of their family or carers, to ensure that these changes are identified and their consequences averted. In addition, remind them that alcohol increases the risk.